L.P.
Hi D.!
My now 5 year old son has always HATED tags. He always asks me to cut them off. There are certain ones that don't bother him for some reason. But especially clothes from the Disney store (before they started just printing them on the material itself...what a great idea) they especially bother him. There's like 2 or 3 tags usually. Anyway, I never bothered writing on the clothing the size and my 2 year old is now wearing all hand me downs. You usually can guesstimate the size. Every once in a while I wish I knew but in general it doesn't really matter. Plus I remember how old my 5 year old was when he wore most of it so that helps. :)
That was a good idea though someone else left about using a fabric marker or something if you really want to know. I don't know if I was much help, but just wanted to tell you that we had and still have the same issue. He had LOADS of beautiful hand me downs which are ending like now. I need to go shopping now and I think I'll stick to old navy and gap or whoever makes those print on the material tags.