This will probably come off as mean spirited. I don't know that there is any specific dividing point though, because it's all about context.
A lot of parents can be compared to when babies are born. They get super excited when they roll over for the first time, crawl, sit up on their own, etc. They literally don't know how to reel themselves in. Is it any less annoying? No. But I don't think there is any purposeful intent.
On the other hand, we all have seen exactly what you're referencing. And I agree, a single cell clip, pic, tweet/post, or two great. Posting over and over and over...not so great. At least post progression. Hey CP got her layout. Months later, CP has her full. Great. Nobody really needs to see 10 videos of learning a back handspring. And the people that do, are probably just the same people doing the same with their kids.
I posted a back tuck video probably 3 yrs after it was learned. At that point, only because it was funny to look back at it. If you have something amazing, like Titus the basketball shooting baby, then post it up all you want! Otherwise try to show a little restraint.
Additionally, and semi-related, name dropping is super annoying. I don't get why everything somebody says has to either mention they belong to gym xxx, or are part of team xxx, or how their cheerlebrity teammate is so nice and down to earth, just to let you know they know them!