The show - which opened at the Shaftesbury Theatre last month - is looking for three new pairs of children to play Tommy aged four and 10.
In the musical four-year-old Tommy is played by a six-year-old girl and the 10-year-old is played by a boy. The child stars are allowed to perform in only 40 shows.
Little girls clutching their mothers' hands queued nervously at the theatre's main door waiting to get through the first hurdle - a height test. Casting director Suzanne Smith would only consider children under 3ft 11in to play a four-year-old.
After the first set of auditions Lacey Crouch, seven, from Eltham, south-east London, beamed with pride when she was told she had passed. "It was all easy and lots of fun," she said.