If I file a Visa Petition for my married son, do his wife and children also get green cards?

Yes, in most cases dependents of the primary alien will also be given green cards. There may be special rules for children who become 21 before the visa interview. In some cases they “age out” and are no longer considered dependents. The Child Status Protection Act (CSPA) in some cases may allow older children to still receive a green card.