It's not a topping, but I suggest practicing your skills at making pancakes in letters, smiley faces, other designs. It will be a bigger hit than toppings with the kids. At 31, I still love when my dad makes me a pancake in the shape of my first initial on weekends at my parents' house.

Bananas! Slice in half then in half again and heat up in a pan with a little cooking spray. They get all caramelized and delicious. Also nuts or nut butters are awesome on or in pancakes. Also, not sure if you want the actual pancakes to be different flavors, but pumpkins pancakes would be great right now. Good luck, sounds like a fun party!

yogurt, jam or jelly, nutella, peanut butter, applesauce, i'm getting hungry...

speculoos, cinnamon & sugar,nuts, whipped cream, sprinkles, reece's pieces, caramelized apple slices, ice cream... Just think like a kid, if something seems like it would be way too sweet then that means they'll love it. As for sides - what about veggie sausages?

I recommend home made fruit sauces. Just fresh or frozen fruit, citrus zest (optional), about 1/2 to a cup of sugar (to taste) per pound of fruit. Cook over medium heat until mushy, then blend, and strain if desired. Relatively cheap, and you know where each ingredient comes from; which, incidentally, allows you to avoid allergies easier. I took a raspberry sauce like this to a school class iced cream party for my daughter and wowed each parent and the teachers with it's flavour and simplicity. Also a great way to make use of seasonal fruits.

Update: I forgot to add about a cup of water. Other wise it may be too thick to be a sauce.

Dulce de leche and bananas.

Also, if you want to mix up the pancakes themselves, buckwheat pancakes and cornmeal pancakes are yummy.....

My all-time favorite pancake topping is applesauce!

Banana, lime juice, creme fraiche and a drizzle of maple syrup. I first tried this at a crepe stand in Dublin, sounds weird but it totally works. Or fried eggs and tomato sauce/salsa for a savoury option.

A little butter is always delicious on pancakes - throw a stick with some honey and a pinch of salt into a food processer and cream together. Sweet and a little salty and delicious! Also homemade fruit compotes are a delightful alternative to maple syrup.

ice cream and fro-yo. seriously.

sugar & lemon, dulce de leche, lemon curd, chestnut cream (maybe not for kids though?). Also, I haven't tried it, but The Galley Gourmet site has a recipe for gingerbread pancakes that sounds wonderful !

Don't forget some savory toppings! Sauteed mushrooms or garlicky spinach with a poached egg, chili (especially with corn pancakes), or sausage gravy would be delicious.

I'm excited for you ... the kids will LOVE this. I've done this several times for my daughter after sleepovers using either pancakes or multi-grain waffles. Decide on 4 -5 toppings & a couple of sides & then, sit back and enjoy their joy!
Toppings: variety of baking chips (semi-sweet chocolate, caramel, butterscotch, etc.), shredded coconut, fruit sautéed in butter with cinnamon (peaches, apples, pears, etc.), thinly-sliced banana, pumpkin butter, warm maple syrup and ... chopped nuts only after checking with the parents to ensure that none of the children have nut allergies
Sides: thin-sliced, tart apples & sharp cheddar cheese, veggie burgers sliced into wedges, string cheese, warm boiled eggs
Beverages: most-definitely water (to balance out all the yummy, rich, abundant flavors!), milk, juice, smoothie
Oh ... and a tiny bit of unrefined coconut oil is a yummy alternative to butter on pancakes, waffles & toast