Here is my nephew. He is one strong kid. He has been amongst the top runners in his school. He ran 80 miles. Here he was working out with me in the gym in Gilli Lankan Fushi, Maldives. Whatever, task I gave him, he superseded my expectation.
Disclaimer: Do not make your kids attempt all this. He was doing it under watchful eyes of a trainer (me). He did warm up before and stretch later. Gilli has a policy of "No shoes". They do provide shoes inside the gym but they did not have shoes of his size. They were amazed to see such a young boy working out enthusiastically in the gym with adults and out beating them.
On Foam Roller
With Kettle Bell.
4kg Dumb bells.