School jumpers?!

My son started nursery 2 weeks ago and on the second dayhis jumper was bobbly,it has been washed once on a 30 but was bobbly before it was washed and then i just rub it down with a cloth other days. How can i stop it from going bobbly im so confuzed none of the other childrens jumpers look bobbly?!? He wears his coat to school so it does rub against that but this is terrible bobbly not just bareable bobbly :( any ideas?