Angel food cakes are really yummy. You can put cool whip on them instead of heavy frostings and put fresh fruit on them. You can do a sugar cookie pizza too, where you make the sugar cookies, make one HUGE cookie on a pizza platter, when cooled put cool whip on it and slice up fresh fruit.
You can also do lighter versions of sundaes, get frozen yogurt with less sugar and do toppings like light caramel and fresh fruit and sprinkles. Have a sundae bar as kids love to build their own.
You can also do bananas/strawberries on sticks frozen dipped in chocolate.
When baking you can use natural applesauce instead of sugars in a lot of them which still gives it sweetness without a cup of sugar.
Sugar in it's real form I truly believe is better then substitutes. I think in moderation and making sure they don't binge on it is the best way to prevent too much in their systems. I think on special days like Birthdays just keeping it low key like maybe watering down the juices, getting No sugar added juices and lighter cakes. It is the frosting that is the killer on bday cakes!
Ask your Pediatrician too what they deem as good levels daily of sugar with your family history. I limit juice to one glass at breakfast, I did sugar free popsicles for treats but my Pedatrician said that substitutes are not good and there isn't relevant testing on them to see what the harmful side effects later could be.