My youngest son doesn't like oranges, but I suspect it is primarily a gripe with the texture of the membranes. I bet he'd like them supremed! I never knew that was what it was called. You learn something new every day!
If he's old enough to be trusted with a knife, teach him to supreme his own after the first few go down well... it's a great technique, but it's time consuming. With grapefruit, BTW, you've got bigger sections and sturdier membranes, so you can peel the fruit and deconstruct it as you go along, separating chunks of fruit from the membrane with your fingers (no need for a knife).