I did dress my boys in matching shirts every day, for exactly the same reason SunDevilDaddy stated. I chose shirts from the
Disney store or online disneyshopping.com for Disney themed shirts. I bought the brightest colors they had, figuring it would make the kids easier to spot in a crowd.
We had several sets of orange, a bright yellow, a more golden yellow, a couple lime green, I think a red, and a set of matching turquoise shirts for the whole family. DH wasn't big on the matching shirts for the adults, but thought we looked pretty cool all together.
We saw many big groups all wearing matching shirts like ours, and it did make them easy to spot. One group must have had like 30 people!
Along the lines of keeping kids safe, I also printed up some address labels on the computer, just typed in our name (not the kids' names) and DH's cell number in case the kid got lost. I stuck it to the inside of their shirt so it woudln't be seen unless it was needed.