Winter Clothing and a question

I have learned from experience that one of the key elements to staying warm outside is your base layer. A few years ago I replaced my cotton long johns with a polypropylene base. It has worked quite well for me and now I want to get some for my family. Unfortunately, I can't find any small enough for my 2 year old. She is currently in 2T. If anyone has any suggestions, could you leave a comment? Thanks.