Julie,
that was it as information goes - not very much I know.
I were going to make a guess I'd say that Simon and the older Thomas were contempory, maybe brothers, and that they moved to the parish some time after the birth of your Thomas. One thing I did notice was that a Thomas Childs was a regular witness to marriages from about 1770 onwards, signing his name and writing out the entries - perhaps he was the parish clerk, yet the Thomas who married Mary Copsey couldn't write his own name! Perhaps a trawl through the IGI for Simon and Thomas Childs would point you towards another a parish? Its always worth a try.
Neve