A distraught mum rushed into the back yard, where eight-year-old Tommy was

A distraught mum rushed into the back yard, where eight-year-old Tommy was banging on the bottom of an old upturned tin bath with a poker.
"What do you think you're doing?
" she demanded.
"I'm just entertaining the baby," explained Tommy.
"Where is the baby?
" asked his Mum.
"Under the bath."