If you go early in the day, like before 2pm movie tickets are like $5 each where I’m at. Maybe she could just take her kid that’s having the birthday if it’s that big of a deal to him. Then take the other kids later. I’d have one on one movie days with my 4 kids. I’d also take them all at once but it’s important to have one on one time with each of your kids without their other siblings all of the time.