Does this kind of stuff really make you mad?

I know this is petty but we live in a rural town with a community pool. My two youngest (5yr old twins) take the same brightly colored inner tubes to the pool each time we go. Yesterday we were the only family there with inner tubes and they generally have them on the whole time, so duh, it is obvious they are ours. Everytime we go it seems someone takes and uses the inner tube the second it's put down. This drives me crazy that they don't even ask and their parent also is usually right there. I don't want other people using them as when they bust it then I get to make the trip to Walmart for more to appease a disappointed child (my own). I know some of this is to be expected, but it makes me mad, especially with the other child's parent right there that other kids never ask. Yesterday mine had not had a nap and one had a meltdown, so it was time to go home. So, not only am I trying to get two little boys, one crying to leave, get all our stuff, I get to go ask for our inner tubes back from two tweens.