If you aren't worried about looks, you can add the fresh fruit slices right to the bottle the fruit juice comes in.
If you want a little nicer presentation, pour the juice in to a pitcher and then add the fruit.
Cover and let sit for a few hours to overnight.
To serve, pour the fruit infused juice in a glass and top with approimately 1/2 cup of lemon lime soda.
Can be served over ice.
Garnish with some of the fruit added to the juice.
Notes
Obvi, make sure you don't have your own sangria hanging around so the kids can mix them up.
You can stick to just a few types of fruit in the non alcoholic sangria or add a whole bunch of different kinds. What I love about this is that you can change it up a little bit each time you make it for a slightly different flavor profile.
I prefer to use store-brand Lemon-Lime soda. I feel like it has more flavor than some of the name brands.