AI'm getting nervous about baking my foster daughters birthday cake on Sunday (actually baking today and then freezing) I plan on using box mixes. I'm not a pro! Lol.

I plan on doing chocolate then strawberry then vanilla, chocolate then strawberry. With strawberry buttercream frosting.. She doesn't like vanilla but loves strawberry and chocolate. So I figured I can get away with one layer of vanilla

My worry is that the cake will fall apart if I don't do something to make it like the Wasc I'm making for my daughters cake (her bday too that day she's getting a rainbow cake) I've already tried the wasc and we all love it.

So should I add anything to the choc vanilla n strawberry mixes to make it sturdy and as yummy as the wasc? I read recipes to use yogurt instead of sour cream for the strawberry. I thought strawberry yogurt and then vanilla yogurt for the vanilla. But what about the chocolate?

I'm finding all kinds of recipes but don't know what to choose. The girls are only turning 7 so I'm sure I'm worrying about the outcome way too much lol

It should be fine, but honestly, if you're worried, I'd go ahead and use the WASC method for all of them.  It's not that much more effort than just the box mix!  

Ayou could add dry chocolate pudding to the mix for chocolate flavor and put chocolate buttercream next to that layer in the cake. if you are using wasc it should not alter your results. i enhance my box cakes with pudding and sour cream all the time.