I used to give my kids rhubard and they were ok.
Try to choose a naturally sweet one or if you must sweeten it you could use a little honey.
In my experience they can be given any food that you eat yourself; just try them with a little bit to start with.
I never gave mine extra sugar in food or drinks; they only develop a sweet tooth because of what they are fed.
My elder child didn't have sweets until he went to school and all the other kids had them. He hadn't tried them so he didn't miss them until then, for treats he had grapes, banana, etc.