"Just bought this costume for my 4 yr old who wears all 4t clothing (and its baggy in him) ..i went according to the size chart on this site, and it should have had plenty of room ...however, it barely fit and by barely I mean I couldn't even Velcro the back and forget about trying to wear sweats underneath it... The costume itself was so adorable and he absolutely loved it... I just exchanged it for the 4-6 size and I'm hoping that wont be way too big"