I realize people want their kids to behave in public. But this week, I've gotten a bit weirded out with parents making their kids say "thank you" to me after I vaccinate them. It seems well-intentioned, but a bit heavy-handed. Because I'm pretty sure that from the kid's perspective, they've been dragged to a strange place and held down while a lady they don't know just stabbed them with a needle--not exactly something to feel thankful for.
If the kids don't hit/kick/scream too much (and how much is "too much" completely depends on the child in question) I give them a sticker. (Or an extra Band-Aid, if we're out of stickers.) Having them say "Thank you for the sticker" seems appropriate (Although the Happy Hospitalist seems to have issues in this department) but forcing the kids to express unspecified gratitude confuses me.