Complex sentence: As the supply of silver thruppeny bits (see threepence) slowly disappeared, sixpences replaced them as the coins that were put into Christmas puddings and children would hope to be the lucky one to find the sixpence, no doubt also encouraging children to eat their pudding.
Split into simpler sentences: As the supply of silver thruppeny bits (see threepence) slowly disappeared, sixpences replaced them as the coins that were put into Christmas puddings. Children would hope to be the lucky one to find the sixpence, and were no doubt encouraged to eat their pudding.