I don't have a little boy to test my theory on, but I think you can dress a wee lad up in dazzling highland attire for fairly cheap via Walmart or the like. The only thing you have to go elsewhere for is the kilt, the sporran, and sometimes the hose. (knee high socks in the little girl's section would work in a pinch)

See if I had a wee lad of 5 and I had to dress him up for some fancy function I would simply get him a nice dress shirt of a coordinating colour with his kilt, some regular dress shoes, maybe a zipper tie, and a vest that is 3 or 4T depending on how tall he is. See...the younger size will be shorter and just perfect for kilt wear.

--Chelsea McMurdo--
Whose daughter turned 1 year old today