To echo what ajlafleche said, get the tables up high. I don't know how many times I've seen people lean across a table to get a better look or take a picture of a model only to have their opened garment drag across a model, camera strap snag one, or purse crush one. Get them up and set up staff to police the tables and aisles. Hold parents responsible for their children. If the kid is touchy feely...hold the parent responsible.
I had to make the comment at a recent exhibit to awaken the parent as to how much it was going to cost them if junior broke the model.
Trophies, well it is nice to win, the older I get the simpler the recognition the better. If I had my druthers, a token such as a coin is far better than a plaque. Smaller tokens are easier to display in the case with the winning model. Plaques for many just get recycled as bases for new builds. I was at an event where they gave gold silver and bronze commemorative coins as awards.
Kids though need recognition is a tangible way. Certificates and trophies are a must. Just remember they don't have to be big and expensive...and remember parents are the ones who end up lugging it around afterwards! Keep It Small but Shiney!