My daughter requested button up shorts pajamas to match me. I sized up per the recommendations and probably didn’t need to. My daughter is currently 6, and wears a size 7 usually. She likes things loose and baggy. I went with the size 8-9 thinking that would be up 1 from her usual and they are huge. She still loves them and the shorts don’t fall down, so we’re just going to keep. If I buy again we’ll go with the 7-8. She is an extremely picky child when it comes to fit, fabric etc. and she is in love with these!