My 4 1/2 year old did insanity with me today :)
I did Insanity today (Cardio Power and Resistance) and my 4 1/2 year old wanted to do it too. She had tried it in the past and would just do some random exercises (jog, but kicks, and stretching) but she did the ENTIRE thing today! Okay minus when the dog got interested in me working out and I had her put him in his crate. But she did every single exercises (4 year old version but some of them were pretty good form). I was very impressed!