Tony@mychildsafety Posted: 5/23/2011 4:34pm PDT In general, your child is ready to make the move to a booster seat when she is four years of age, at least forty pounds and has grown too tall for her car seat. suzannekane Posted: 5/26/2011 1:19pm PDT @Tony@mychildsafety- thanks for the comment. Makes it a little easier to understand in parental terms. Key words are "in general." There are always exceptions.