DD is 2 1/2 and we have a newborn due any day. We currently only have one car seat between my husband an I for DD - the Britax Boulevard 70CS. I was thinking about getting a second convertible car seat now so that DH can take DD to daycare, etc, while I'm no maternity leave. Once the new baby is big enough for a convertible seat, we'll already have it and we'll just be back to one seat per child (which is fine). I know seats typically expire after 5 years, so I'm just trying to figure out if we would make it far enough with the new seat for the new baby if I get it now. What do children move to next? A booster? What size/weight do they have to be for those?