A little more unsolicited advice -
HS Graduation - If pomp & circumstance is going to choke you up then desensitize yourself to it. Start playing it around the house for 2-3 days before graduation. Then you will be smiling and not bawling. My youngest graduated it in June and I started humming it today.
Graduation, Senior awards and all the Parties: Be proud of your kids, but be humble. They haven't done anything yet. If they have a classmate(s) who is enlisting, make a point to seek them and their parents out. Don't brag about your kid- they probably already know, instead thank them for their and their child's service. These kids will be in the fire a lot sooner than yours.
If you school acknowledges your child then ask if those who are enlisting in the military can be acknowledged. OR - have your child ask.
Don't forget about the other parent and siblings - Christcorps is right - Dad's have a hard time with their kids leaving. If you are divorced - make a point to include the other parent. Set your differences aside and just be parents to your kids.
Siblings - younger ones have a hard time. When my oldest left, my youngest was 10 and she cried and cried. If they go to I-Day/R-Day they may cry like babies.
Everyone knows the family structure is changing and it will change. A new pecking order will be established, the younger one's may think they will never see their sib again.
Sometimes - being a mom means being strong. But as women we already know that.
USNA69 - very true - you are moving into a new dimension in your relationship with your child. He/she will always be your child and you feel that now but soon will be a great friend - for me - this is one of the greatest rewards of parenthood. Embrace it.