what age do you have you have to be to go in

With the exception of the lion king, I haven't noticed any young children. I'd call the hobby center. I'd never bring a child under 13 to anything not child centric. People pay a LOT of money for tickets, and I would never take a chance on disrupting their theatre experience.

It all depends on the event their hosting

"As a courtesy to other patrons and performers, admittance is not allowed for children 5 and under unless the program is child/family specific in nature." -The Hobby Center for the Performing Arts

Most shows have minimum age limits which would be listed on their websites (like 5 yrs old for the ballet). If it's not listed them I'd suggest calling Hobby, who i found to be very welcoming of questions.

Depends on the venue I would imagine. I've never seen children attend events I've attended.