I actually don't have much of a problem with other moms bragging about their kids. In fact, it has to hit a pretty obnoxious level before it strikes me as anything other than necessary, earned, and understandable pride. Not everyone feels that way about kid bragging, though, so there are just a few rules I think every parents should follow in regards to the times it's really OK to brag about your kid.
Even though I'm pretty lax on the whole "constantly bragging about your perfect kid" thing, there are days when my kid hasn't slept well at all, and I'm spending a lot of time in my head wondering when my kid is going to hit that one milestone that every other baby seems to have hit, as a result. On those days I wish I could wear a sign asking all other moms not to brag too much about their kid. It's important for us all to remember that not every kid hits every milestone just when you want them to, and that constantly bragging about certain situations only stands to make the parents around you feel like garbage.
The key to not making other moms feel bad by exclaiming about your kid's successes is to know your audience, and keep in mind that you're trying to express pride about your child, not make anyone else feel bad. So, with that in mind, here are a few times when it's absolutely OK to brag about your kid. You know, just in moderation.