Encourage experimentation: failing is part of the learning process. Help the children to see that professional sculptors make lots of models which they discard.
The Towner Art Gallery in Eastbourne funded visits by local artists to West Rise Junior School. See if a local museum or art gallery can put you in touch with a sculptor who is willing to visit your school to talk about hisher work. Or contact the Royal Society of British Sculptors education office. Tel: 020 7373 5554.