Here's a template to print your own money (goes down well), and some ideas for games you can use it with. Here's the template. Change the details and gogogo.
MES English has a popular idea called Grammar Casino, which involves betting on true or false to some right or wrong sentences. You can do the same thing getting your kids to write missing words in gaps; betting on their own confidence.
In fact you can slip these notes into a lot of activities from T/F tests to Shopping lessons. The world is your oyster.