It ... can? It really depends on the children, the dynamics, and other factors (so I'm not saying "have another kid and everything is fixed").

It does increase the network, so that if one kid doesn't want to play, the other might. Sometimes all the kids are playing together, sometimes one is off doing his own thing, sometimes there's still a meltdown.

Three might be the nadir as they outnumber you but each kid only has two other kids. But when older you likely can deal with one kid at a time and the other two play.

If it makes you feel better 4 to 6 is about the worst for "normal" kids, too, as they know that the outside world is something they have influence over but can't always control the way they want to.