The ones here in Colorado have sighs stating “No one under the age of 18”, pretty much PERIOD, at all in the casinos.
Though when I visited recently to Cripple Creek (first time I ever went in one) there were young kids with parents in the hotels. And they were eating in the restaurants.
In my state, the minimum age to enter the gaming area is 21.
Plenty of adjacent areas, though, where families with small children go.
Fortunately, these areas are roped off with theater ropes.
And we are quick to cite the casino's security staff if any minor crosses the line.