If your child is 10 years old and has been getting bullied in school by another 10 year old what can be done about this?

My 10 year old son has been bullied in school by another 10 year old.The kid has kicked my son in his groin,told the principle they just spoke to him about it and gave him one day in the quiet room.My son has been called hurtful names and had a baseball thrown at his head,was at recess the kid ran body slammed him.All things were told to either a teacher or principle but nothing was really done about it.The parents don’t care I know their 10 but no child should be bullied and have to deal with it. I did go to the local police department to talk about it he said, because they’re 10 it’s kids being kids.If they were 14 years old they could do something about. My son shouldn’t have to put up with this this kid kicked him hard in the groin and he got away with it it’s just not right! Now another school year is approaching and I will be worried sick about if this kid will bully him this year. The principle knows so I don’t know why they don’t take this stuff serious it’s not fair!