I have the same question, thank you for asking it!
I googled it. Apparently it's until they don't need diapers anymore / are potty trained
When they start potty training as the poppers get in the way. The bodysuits I find hold the nappies in place.
Whenever you want them to, there’s no right or wrong answer
We swapped my little girls bodysuits for the ‘big girls’ vests when she started to use the potty/toilet
My little one is 15 months and still wears them during the winter esp long sleeve ones,then girls vest during the summer.
We stopped when we started potty training at 2 years 3 months
We swapped to “big girl vests” at 18 months ❤️