Amazon EssentialsBoys and Toddlers' Polar Fleece Vest

What size should I order for a slim, average height almost 10 year old?

Is there a summer light weight version of this for warm weather?

Could a petite woman wear this? i typically wear a xs or s, and i can’t find a vest for women like this on amazon. would xl work?

Is the night navy just light navy blue or darker?