My son will be getting out of prison for sexually messing with an under age kid (witch was consential)what are the laws when he gets out.

Depends on where you live.

Likely, He will have to register with the states sex offenders list. Also he will be given rules of how far to stay away from kids, playgrounds, schools, etc. If they don't he needs to ask.

You can type his state + Megans law in the search engine

What state? Generally he's going to have to register as a sex offender with the county as soon as he moves there. And every time he moves his residence he has to re-register. There are other things that he has to do, but the residency one is probably the one that the police take most seriously.

Yes, it is most likely that he will have to register as a sex offender, and keep the state informed where he lives and not live near certain areas.
It will depend on the exact charge and the state you live in, ( if in the US)

Oh and also he needs to be careful about girlfriends because I have heard of Child Protective Services taking children away because the boyfriend has sex offenses.

Yes, knowing the location would be helpful. But, don't you have any documentation as to what was required of him by the judge for him to do after he gets out of prison?

Thanks!