DD1 is maybe 32lbs, and will be 4 in march. DH suggested getting her a booster when DD2 is out of her infant carrier. I threw a fit saying it wasn't safe, but really I have no clue. what are the height/weight/age requirements for a booster seat? I just don't want DD1's safety to be negatively impacted in any way - and I'd rather by another car seat just to be on the safe side.