I make their colas and root beers. It makes for a halfway decent soda and it gets my kids involved with my brewing, taking into account their short attention span.
Add about 25% more (cane) sugar than the instructions ask for. Add 1/4tsp of maltodextrin per gallon of the root beer to improve head retention.
Then I force carbonate using a carbonator cap available from LHBS.
Ex fermentum, scientia.