Onesies- when to give them up?

We call onesies all-in-ones here.
I only ever used them on my kids when they were little babies.
I never used them after the babies were 6 months old.
They were very good for keeping them fully covered in the winter.

hmmm...you have a point there. My older one was potty trained quite early and I didn't really have a problem with onsies then coz he would tell me he needed to go and wait for me to get the onsies open and we weren't using diapers.
But our younger one is 13 months and I've started training him. I can see I'll have a problem with onsies. I usually don't use onsies at home...but it sure can become a nuisance like you pointed out.