Purchased a 4 for my 3 yr old (nomal clothes size is 4T) and it was way too small, returned it and upsized to a 6 and it fit him perfectly. My only minor gripe is that the sizing is somewhat small. Nothing has failed. --Im not a DJ or an audio expert. These strobe lights are great, now when my husband is out plowing he can be seen a mile away. My unit arrived with a slight dent in the door at the top. But it serves its purpose and Im okay with it. Would I do that again? Absolutely NOT. Even compared to a pricier set I have. I originally bought these as a gift, but would be too embarrassed to give them.