Too bad about the plastic restriction impacting gift selection. (Personally I strive for minimizing plastics, purchasing a minimum of new plastic items that will serve good purpose. But I respect those with stricter roles.).
How about wooden puzzles?
I checked about tinker toys, but they’ve been plastic since 1992.
The kids are 5, and while nice, these toys look like they would be more suitable for toddlers.
There is plenty of gifts for girls of all ages and for boys younger than 4 and older than 8, but this is a hard age group to shop for without encountering any plastic parts! 
Marble Run Toys, 60 Pieces Wooden Classic Ramps Track Building Construction Set for Children Toddler https://a.co/d/foceAeb
I don’t know if there are any kid’s scooters without plastic (I’m thinking plastic wheels may be acceptable?), but maybe?
Thanks! Looks good, just one hesitation… one has a baby sibling, so mom might not approve of marbles! I’ll ask.
Check out some online retailers with Montessori toys. Also, Etsy is a great place for wooden toys. You could also consider a membership to an aquarium or children’s museum near their home.
Drum sets? 
No plastic wheels either! It is crazy, really.
Thinking of a heavy metal band set! 
Another idea is puzzles - maybe even like 3D dinosaur puzzles (or other figures!)
Or get them a soccer ball they can use inside and knock all the glass objects over with …those parents will WISH they had plastic!!! Just kidding.
My kids used to have a large floor puzzle they loved.
Would they allow games?
This one is a good one, and all ages really can play. It’s a card game. I hope the container isn’t plastic!
This gets good reviews, but targeted to 7 and up.
But maybe a board game or card game or puzzle is the way to go.
https://www.amazon.com/Fire-Hole-Plastic-Free-Eco-Friendly-Biodegradable/dp/B0B4WQZYMZ?th=1
Jenna, checkers, Chinese checkers? Maybe you can find Aggravation with no plastic?
Art supplies. Clay + tools. Watercolors + paper. Nice markers + sketchbook.
Bead sets? Wooden beads? Kids are wildly into making bead jewelry- even boys. Thanks to Taylor S!
Have you looked into Tegu, which is magnetic wooden blocks? Because of the magnetism, the blocks can stick together better for building structures, vehicles, etc. But they’re also large enough that there shouldn’t be issues with 1-year olds. (Manufacturer’s site, Amazon’s search results).
Hey Clay has sets of modeling clay to make various types of animals: FatBrainToys’ search results…though they’re also available at the jungle store).
Keva Planks are another type of block, but these are thinner and narrower and can provide more flexibility in what one builds. Here is the manufacturer’s webpage with project ideas, but these are available at the jungle store, too.
Do they like acting or role-play? Props or costumes could work.
If they’re artistic (or thinking about being artistic), then there’s tons of art supplies, perhaps accompanied with a book (I know, I know) on how to draw certain things?
If they’re into nature, perhaps a magnifying glass or bincoculars or something that would work with that?
Wooden Marble maze? (Sometimes called a marble run). Wooden jigsaw puzzles?
How about Camelot Jr. It’s a 3-d wooden logic puzzle. Really cute and my kids loved it.
https://www.amazon.com/SmartGames-Cognitive-Skill-Building-Featuring-Challenges/dp/B01MRUSZ1Y
My kids liked these large cardboard blocks long ago.
My brothers and I played with blocks like those for hours at a time in the 1960s. Then my kids loved playing with the same ones when we visited the grandparents. I doubt today’s are as sturdy but I second that they are fun.
My D has a serious boyfriend who is not coming for Christmas but we didn’t want to ignore either. We sent a joint package to them with tickets to a show and an “Adventure Challenge Date” book. The book looks fun - it’s basically a book with scratch off date ideas. You pick one with a little bit of info available like price range, length of date, etc. Some of pretty simple and some silly but it seems like a fun idea.