Just a personal opinion, but we don't use first names, or even 'Mommy' or 'Daddy'- we just use the family name 'Thomas Family'. I get too nervous that someone would see our name, or our child's name and call it out and our daughter get caught off-guard (it's Disney, it's a pretty relaxed environment, but it can still happen). She's 4. Not to mention, we get our t-shirts screen printed locally, and there's an extra charge for each change you name (different names, number of colors, etc.)- so we keep it simple for that reason, too. Just my $0.02.
Last Year we did 'Walt Disney World, 2009' on 2 different lines in Waltograph font on the front right chest of the shirts, then a Mickey on the back with 'Thomas Family Vacation' below it. Works for us- 1 color imprint, same imprint on each shirt- we got compliments just the same! Good Luck with your shirts!