We tried a sz 4 and 5/6 for our 5.5 yr old who wears a size 5 in every other brand (he's tall and thin). The 5/6 were enormous. the shorts came down to his calves, no joke. and the waist was huge. The shirt would have fit fine, a little boxy. We exchanged for a 4 - the shorts were still way too long and also too big at the waist. this time the shirt was too short, but still boxy. The material seemed good and the style was cute, but the fit was just completely off. The oshkosh mesh shorts sz 5 fit perfectly.