I don't know if trek has it too, but if your 2 y.o. really wants to ride the TAB, you can buy a backrest for Adam's TAB ( http://www.amazon.com/Adams-Backrest.../dp/B000SMS7IC ) and start at earlier than normal age (might need blocks on pedals too).
Also there are tandem TABs (for two kids) available ( like this: http://www.trail-a-bike.com/products...folder-tandem/ )