S.S.
Despite my son's high energy, even at an early age, he could sit through theatre performances. By the time he was 3 he had seen Lion King, on Broadway twice. At the amusement parks he will sit and watch every show from beginning to end. At age 4, I lied and said he was 6 and snuck him into "Into the Woods" on Broadway. Other kids I wouldn't even think of doing this with. I think it really depends on the child and level of interest.
Have fun,
S.