T.B.
When my youngest went through this, at about the same age, we found a small booster at walmart for like $15 that is great. I think it was made by Graco. It straps into the adult chair and has a safety belt to keep them safe. It is also foldable, like the captains chairs that you can get for adults. The one we bought came with a carrying bag, and we take it everywhere. She is almost 4 now and still loves to sit in her "big girl" chair.