First check that he doesn’t have a rash or anything… Then simply say quietly, whenever he’s touching himself: “That’s something we do in private.” Don’t make too big a deal of it, but repeat it firmly every time.

Think it’s a normal thing developmental wise. As they get older it often reduces or stops. I have a 3,5 yr old girl with Down syndrome who does it a lot. Not only that, she also like to touch and eat her poo. This is not uncommon for kids with a delay, but it’s not something I encourage.
One thing what might be good is to teach your kids privacy and not to do it in public.

Yep it’s just a phase. I ignored it. Sometimes making an issue of it makes them more inclined to do it

My 3 year old nephew kept doing it, I told him one day that if he kept playing with it, it would fall off. Maybe not the best approach but he stopped playing with it.

A. How much exactly do you class as too much
and
b
B. Teach him the importance of privacy and make sure everyone in the house respects it also if it really is to much a.k.a he spends most day doing nothing else or he does it at school then go see your GP about it

Also whatever you do make sure you understand 3 times a day is perfectly normal for a young man and there is nothing wrong with it.

Do not shame him about it never tell him it is wrong

Having had 3 boys I agree with the other answers it is normal. Without bringing to much attention to it they soon outgrow it, but if they continue in front of other children you need to address it early as they could end up been teased at school.

Depends on how young .. if older young there is links on websites to help

Boys can be shockers thank goodness as they go to school it’s stops quiet a lot , 4 y o at the moment doesn’t stop I just say hands out of your pants thanks and we just go on with what we were doing and he stops and doesn’t think anything of it , so I don’t think I am making a big deal if it just letting him know

I didn’t make a big deal of it. I said to my son it’s ok to be curious but you can’t touch your willy in front of people or in front of the TV. And we would have a little giggle I would say you can do it when your older in the shower but not when your in the Lounge room etc. make it a but light hearted

Hes a boy and im afriad boys do this, its something new to them, i was worried at first as when my son was 2 and a half he started playing with his all the time the doctor said to me “its normal” he did it for about 6 months then stopped.
Try not to make a fuss about it maybe just move his hand away but without saying anything.

without knowing how old he is it is hard to give you a definite answer. here is a link that may help you. It outlines what is “considered normal” according to different ages. Bit of a sensitive topic but great that you are handling it with sensitivity. Good luck
http://www.nspcc.org.uk/help-and-advice/for-parents/talking-about-sex/sexual-behaviour-of-children/child-sexual-behaviour_wda96782.html