Kids love their own soap. You can make your own moulded soap very easily.
Buy some clear soap from the supermarket. Chop into small pieces and place in glass microwave safe jug.
Heat in the microwave until melted. It may take 60 seconds, but heat for 20 seconds at a time and swirl each time to dissolve evenly.
Pour into silicone moulds and leave to cool before popping out of moulds (1-2 hours)
Pop out of the moulds to use.