Given SFO as the starting point, with so much to see and do in the environs, I’d be more inclined to stay closer to home i.e Half Moon Bay, wineries, Russian River, Santa Cruz, Pebble Beach etc.
I have a friend who’s taken her grandkids from the east coast to Hawaii multiple times. (Starting before first was 2).
I think Maui would be an excellent destination from SFO. There are tons of things to do, including verynice beaches, where kid will have great fun.
Ko Olina resort on Oahu. Rent a condo at the Beach Villas through Ola Properties. We had a grand time at one of their condo rentals. No resort fees, and you are right on the beach with a swimmable lagoon and lots of soft sand. There is a nice kiddie pool at the Villas right next to the bar so the parents can refill their “anti-toddler tantrum medication” while the toddler is scooping sand nearby. Very relaxing place. Lots of dining options and Costco is just 2 miles away. Load up on groceries and make your own meals! The bedrooms in the tree bedroom condos are quite generous or you can rent a “suite” of 2 adjacent penthouse condos only accessible by keyed elevator so like having your private floor.
We went to Maui when my youngest was 9 months and the big Island a year later. On the plus side, lots to do for kids, pretty easy to get to from SFO, nice climate. But man I still remember dh and I taking turns lying in bed from 4-6am trying to keep the baby from waking everyone else up. Not sure I’d recommend going that direction at that age. I guess with just one kid and a bunch of adults willing to take turns with the 4-6am shift (are you all really willing to take turns with the 4-6am shift?) it’s okay but otherwise it’s going to suck for the parents who are going to be the party poopers wanting to go to bed 3 hours earlier than everyone else (of course, if everyone else is coming from the East Coast it probably all balances out anyway). Or maybe your grandkid is more adaptable to time changes than my kids were.
My D was great traveling at 6 months to 3y.
But one trip I especially remember was an 8 hour car ride at 18 months. Happy as a clam the entire way. Not a peep Stopped at a restaurant and it was like the energizer bunny got overwound. We took turns just following her in a huge circle around and around and around the restaurant outside until she finally wound down. Got some steps in!
Go somewhere close you’ve either gone before or can go back to easily so you can relax without feeling like you’ve missed
anything. Focus on being a family and enjoy those moments together. There’s lots of time later.
If you want that “once in a lifetime” trip (or just want ME time) that you’ll resent missing stuff then leave the kids at home. That’s fine too. Enjoy the adult company. It makes you sane
Which coast is toddler traveler?
SFO!
Not sure I would want to travel internationally (even to Mexico) with a kid this young. Plus, the hassle of getting a passport etc… I would stay in the US. The warmest West Coast place (same time zone) would be San Diego, but no beach weather there for sure!
Florida space coast with Kennedy space center, beaches, warm weather (but you never know in winter), Disney, universal. Lots to do or just lay back and enjoy the beach and food.
We don’t have enough time to make the east coasters’ travel to Hawaii worthwhile; and the toddler’s other grandmother lives there, so the child has already made that journey 
We’re pretty well convinced that all inclusive is the way to go, so all have been put to task to identify required activities and participate in the research.
We did a family trip ( baby also flew from SFO) to Phoenix, Tucson, Sedona and Grand Canyon. Easy flight for the baby from SFO to Phoenix.
Since the OP has eliminated all places in the U.S., I’ll second a couple of other suggestions.
Cabo would be easy to get to from SFO, as would Hawaii (I know that’s U.S. but it’s not continental US). Weather will likely be warm in both places.
DS#1 and wife took their toddler to Cabo last xmas. Made me a nervous wreck, with the safety concerns, water issues, etc.
Cabo’s lovely. We have friends who have taken their twins there every year since they were six months old. My grandchildren have travelled internationally since they were babies, probably the earliest at 4 months. Kids are more resilient than many here seem to think. 
And it isn’t at all difficult to get a passport. I do second the suggestion to get accomodations that allow for separate sleeping area for the toddler. That’s a must.
I was more comfortable with the toddler traveling to Jordan recently than the Mexico trip. I have had more than one bad experience in Mexico, so personally, its not on my list. Glad others feel more comfortable.
@jym626, I don’t doubt you’ve had some bad experiences with Mexico, but I’m a fan of Mexico so I’ll add a countering opinion.
Mexico is a large country, so I think it’s a mistake to paint it all with the same brush.
I remember a few years ago when there were protests in the same state of Mexico as the city we were visiting. Someone asked me how we could possibly visit. I pointed out that there were at that same time violent protests in an American city (Baltimore) the same distance from my home city (Boston) as these largely nonviolent protests were from where we’d be, and asked the person if as a Bostonian they felt personally unsafe. That put things into perspective.
As to post #51, I’d take governmental travel alerts with a grain of salt and investigate further. There are level 2 travel alerts (the same level as for Mexico) in the last 6 months out for Belgium, Germany, France, and Denmark, and level 1 advisories for a host of places like Iceland, Greece, and Finland. England is currently at the same travel alert level as the Baja Peninsula of Mexico.
Mexico does have a high overall murder rate, but it’s lower than that of many popular Caribbean islands, such as the Bahamas, St. Kitts and Nevis, Jamaica, and the Virgin Islands. I just came back from St. Kitt’s and never once felt unsafe. But then again we didn’t frequent seedy bars.
Mexican violence tends to be clustered in certain places and around certain issues like the drug trade. For instance a lot of the Americans who get in trouble in Tijuana are young people who have slipped over the border to buy drugs or to drink at Mexican bars. There really is very little danger at a family-friendly resort.
Are there cities in Mexico I wouldn’t visit? Of course. I wouldn’t put Acapulco or Tijuana on my list. But it may be useful to recognize that St. Louis, Baltimore, New Orleans and Detroit all have higher murder rates than the vast majority of Mexican cities, including Mexico City.
I have gotten traveler’s diarrhea a couple of times in Mexico (as I have a couple of other places in the world) and I would recommend bringing a mini course of mild antibiotics when you travel. The only time I’ve gotten truly sick in Mexico we brought it with us. One of our party started throwing up as the plane landed and and by the end of the week we had all gotten violently ill. That was the only time any of our under-14 kids were sick in Mexico
We have sent all our kids to Mexico on their own to visit their grandmother, who has retired there. I’ve taken a large group for one of my kids’ 16th birthday. I’ve personally visited 3-4 dozen times. Not once have I been stopped by the police, hassled, ripped off, or been witness to or the victim of a violent crime. I’m your typical American tourist-white, privileged, with terrible Spanish and not particularly street savvy, so I’m in no way an outlier.
Thanks for your comments, @Sue22.
There are a few places on my “no thanks” list. I don’t have a strong stomach and I hope my grandbaby has not inherited that gene. Good news, AFAIK, she didn’t get sick in Cabo. But then again, if she did, they probably wouldn’t tell us.
@jym626, we’re all allowed our “yes” and “no” lists. For instance, I have no interest in cruises although I know people who have raved about cruises they’ve taken. Sometimes all it takes is one or two bad experiences in a place to sour us on it, and that’s okay.
@Sue22 - agreed. We are also not big cruise people, but that said, we have taken 2 (one when the kids were younger, and one we took the extended family as a gift). The next cruise I would choose to do would be a French Chateaux/Winery cruise. But thats not for kids If there is a place not on my destination list, but the kids invited us to join them on a family trip, I’d go, even if they chose Mexico. But thats to be with them, regardless of the destination.
Oh, I forgot— I guess we have done 3 cruises, as the Greek Isles trip involved, shall we say, a very large water taxi
Turks and Caicos. We went when are kids were 1.5 and 2.5 and had a great time. Stayed in a condo at the Sands so everyone could go take naps if they needed to. Had a great pool and 2 restaurants and there were lots of other resorts you could walk to along the beach. Beach was soectacular.
You could do the Beaches resort there if you wanted all inclusive.
We’ve also done the Mayan Riviera 5 times starting when our youngest was 6 months old. We love it there and never felt unsafe, the Mexican people were so welcoming. Stayed at 5 different resorts and loved them all. Grand Palladium and Barcelo Mayan Palace would both be great for a mostly adult trip.