Some 3-6, some 6-9 and some 9-12!
Do you mean sleepsuits or all in one outfits? I find George Asda, Primark and matalan sleepsuits are smaller than next, tu & mothercare for example. So when my little girl moves into a size bracket, I go towards the smaller brands, then change them as she grows xx
My LO is still mainly in 3-6 clothes, but everything that has a foot is already small 😂