Columbia Baby Girls Benton Springs Fleece Jacket

My daughter will be 5 months next week and is 16 lbs. For the winter I want to use this fleece for her car seat, would a 6-12 month size be too big?

I'm confused about what size to buy for my 2 year old. She is no more than 26 pounds and is on the shorter side. What would fit her?

can boys wear this ??

Are the sizes similar to carters brand sizing?