A good one for kids (and adults!) is one of my childhood favourites...

Porcupines (Recipe for stovetop but easy to adapt to slowcooker)

420g can concentrated tomato soup
500g beef mince
1 brown onion, grated
1/2 cup long-grain rice, rinsed
2 garlic cloves, crushed
1/4 cup flat-leaf parsley leaves, finely chopped
mashed potato, to serve

Place soup and 1 3/4 cups cold water in a large saucepan over medium-high heat. Bring to the boil.
Meanwhile, combine mince, onion, rice, garlic and parsley in a large bowl. Season with salt and pepper. Using 1 tablespoonful mixture at a time, roll mixture into balls.
Add meatballs to boiling soup. Reduce heat to low. Cover and simmer for 40 minutes or until rice tender and meatballs cooked through. Serve with mashed potato.

Other ideas....
Risotto
Chilli (doesnt have to be too spicy for kidlets)
Chow Mein (mince, curry powder, grated veg, pkt chicken noodle soup, rice, cabbage, garlic, soy sauce, beans, mushrooms, water)
Pea and ham soup (bacon bones, yellow split peas, water, onion, curry powder to taste)