we didn't need any 00000 (or bonds 0000 - their sizing seems quite small in the wondersuits especially) but DS was in 0000 for a few weeks. he was probably in 00 & 0 for the longest & was into 1's a little before his first birthday. but i think it really does depend on the baby - i know a few people whose LOs are in a size height-wise but are so slim that there are only certain things they can wear without them falling off.

i bought mostly 0000 & some 000 before DS was born & then just stocked up when there were sales on as we went along.