A.S.
Just fyi, anyone in PT will strongly recommend against a big wheel as they don't teach them to ride a bike properly. I have a 20 month old and we have a Fisher Price tricycle that converts from a rocking toy to a pushing toy to a tricycle and the seat adjusts for younger to older kids and it is moderately priced. We got it for my older son when he was 2 1/2 for Christmas....he didn't use it much but he has motor delays. My 20 month old is just now starting to figure it out a little bit. They also have these tiny tricycles in stores that you can adjust for very young children.
This is what we have: http://www.toysrus.com/product/index.jsp?productId=2265071
These are the tiny tricycles I've seen:
http://www.toysrus.com/product/index.jsp?productId=2415216