Just depends on where you show. In 4H, our Cloverbuds wear western or english clothes depending on what kind of tack the horse is wearing. Everyone wins. At the big local charity show, I think they place some, but everyone gets a ribbon. My daughters wear jeans, boots, slinky, vest and sparkly belts (bought on clearance at Big Dee's lol) and a helmet. I require helmets on my kids at all times, and as of last year our 4H does too. Very few, if any, people go really "all out" with tack and clothes for leadline at the local shows I've been to.
On the other hand, at Quarter Horse Congress many of the little girls are tarted up like child beauty pageant contestants, with BIG $$$ in clothes and tack.