Disruptive player

Hi all

I coach an U11s boys team, my sons school friend who struggles with some learning difficulties decided he wanted to join the same team, at first I thought great my boy has someone he knows in the team and maybe doesn't feel so isolated. 

I am now finding it extremely difficult to engage this child as he doesn't want to partake in any of the fitness exercises, or any of our drills. He doesn't see the point in doing them? 

What is becoming increasingly frustrating is that he is distracting my son, climbing on him, kicking him or stamping on his feet for his attention, which then means my own kid isn't learning as he is being distracted. 

I'm in 2 minds how to deal with it, as a parent I want to have a word with the kids mum, as a coach I've already discussed his lack of enthusiasm in the last few weeks, I want to help him and try to encourage him. How do you encourage someone who has no interest and lack enthusiasm?

I just feel awful for my boy who wants to learn and play but is constantly distracted by this other lad who just won't leave him alone? 

Any help or advice would be great. 

Thanks in advance.