DD is 1" away from being too tall for her infant car seat. We're thinking of getting the convertible ones installed in Dec if we can-I'm sure she'll be out of it by then. My question is....she's not old enough to sit up on her own yet, so what do you do when you go shopping?? Now I just put her carrier in the cart, but with a convertible obviously that isn't an option. So if she can't sit up in the cart by herself and I dont have the carrier, what do I do?