There's no shortage of television fortoddlers: just switch on the set at 6am and take your pick. Since Teletubbiesfirst suggested that two-year-olds might like something different from their older siblings, the demand for pre-school programmes has grown and grown. Next month, two digital channels designed exclusively for pre-schoolers will be launched. But is it OKfor babies to watch television? Mother of two, Trisha MacNair , offers advice to parents of young children who are keen to keep a firm hand on the remote control. Producer Anna Buckley