CarharttBaby Boys' Canvas Overall Flannel Lined

The description seems to be generic for all sizes - I want to confirm the 2t + sizes do NOT have leg snaps?

I see a 3 m and 6m ect: my question is the size 0-3 months or 3-6 month for the 3M sizing option?

How long Are the 2t & 3t trying to figure out what size my son needs??

Are these a lot warmer than the unlined?