Look for an event that would interest your children. If your children like Sesame Street, look for a Sesame Street production on your area--you could check the scheudle at the Sesame Street site. If the children like singing, look for an appropriate concert to attend, if dance, a good ballet, and so on.
Teach the children how they must behave at the theater. Explain that they must sit quietly while the performance is happening, talk only during intermissions, and applaud between acts.
Let the children know when it is proper to applaud or express their appreciation. At some live theater shows, the behavior can be less formal, allowing the children more freedom to express themselves. At a ballet or a more formal concert, applauding is done only at certain intervals.
Encourage the children to dress up. They can be as extravagant as they would like, for this helps to heighten the experience of attending live theater for the child.
Allow the child to sit on your lap or a pile of coats if the child is having difficulty seeing the stage. Nothing can make a live theater experience more disappointing than not being able to see what happens.
Queue up after the performance to have the children's programs signed by the performers if the opportunity is offered. A signed program can be something your children will treasure for years to come.
Reward your children if they behave well at a live theater performance. This will help to make going to live theater a much anticipated event for your childre--a love that they can carry on in their own lives, and perhaps share with their own children.