Yes, you can use an approved car seat. I was just trying to keep my answer simple. Sorry for any confusion. However, if you're planning on using a car seat, you'd have to buy a seat and could therefore request a child meal (or just opt for the regular catering).

The best thing to do imho is to bring food and snacks onboard for little ones. Actually, it's a good idea for not so little ones if the flight is long. The baby food we carry is indeed Ella's Kitchen, but it's puréed food for babies 4 months and upwards, so might not be ideal for a hungry 20 month old.