car seats

Infants and toddlers should stay rear-facing until they are two years old or until they are taller or heavier than the maximum recommended for the car seat you're using. The longer you can leave them rear-facing, the better. It's something like 5 times safer for them to be rear-facing than forward-facing. Have you talked to your pediatrician about your kids' weight? I'm sure he or she will be able to recommend some dietary changes that could help them gain weight in a healthy way.

"What can I feed them to gain more weight?" Hope your joking hah. Well it depends on your country. In my country I know that when get 14 years old you can sit in the the front seats. I think that there is no matter what the weight is. As for the small kids I think that they can't sit in the front sits. However in the back seats there was weight restriction which is maybe different in the different countries. And if they are under it they have to use the baby/kid seats which have to be bought and placed in the back seats.