Free spirit, lost spirit

Our son Friday1, is a free spirit. Like father, like son.
Today he was invited to a birthday party in the Deutsches Museum. A drop off party. You leave your child at 14:00 in the hands of the museum, the kids are given a workshop on water (very good program by the way, kids loved it), then you come at 15:15 to eat the cake with the kids and the other parents. Great idea. Our free spirit loves cake, so everything fine. But he loves eating cake when he wants to. And at 15:15, our free spirit was not into eating cake at all. He wanted to go on the firemen engine and in the giant guitar exposed in the kids part of the museum. That was not part of the program? No probs, free spirit left the party at some point, without telling anyone. Shall I precise that Friday1 is only 3 and a half years old and still doesn't speak properly yet?! We absolutely don't blame the birthday kid's parents. Because a) everything was fine eventually and b) we were supposed to be there when it happened. And we weren't. Long story short, I felt asleep on the sofa and woke up at 15:19 (talk about loving and devoted mother!). Nevermind, we arrived at the party half an hour too late, to be informed that the kid was gone and, immediately after, to find him in the good hands of one of the museum guys.