My daughter's birthday is in August, we are having an outdoor party and it's going to be hot. The buttercream I make only has unsalted butter and confectioners sugar in it.
I've never used this outside so I'm a little scared it might get hot and melt some.
I was thinking of adding some crisco shortening into it? Would that do anything ?

Can you recommend a different buttercream? It's needs to be super simple, and a crusting one as well.

Butter has a lower melting point. I would never use an all butter frosting for an outdoor event in the summer. You need a recipe using hi ratio shortening it has a higher melting point making it more stable. The recipe I use has 1 1/2 cups hi ratio and 1/2 cup salted butter, 2 pounds powdered sugar, 2 tablespoons clear vanilla and 1/3 cup water. Indebys recipe would also be a good choice for an outdoor event.

I never use Crisco anymore. Since they took out the trans colors don't mix well and it leaves a grease slick in your mouth. I use Hi ratio shortening sold at cake supply stores. It has a higher melting point making it more stable for outdoor events. You would still want to keep your cakes out of direct sunlight. If you can't find Hi ratio purchase Walmart brand shortening. It needs to contain trans fat. Her recipe uses Crisco but I would really try to find the two I listed above. Indydebis Crisco-Based Buttercream Icing
Ingredients

1-1/3 cups Cricso
1/3 to 1/2 cup milk, depending on consistency needed
3 Tbsp powdered Dream Whip (*)
2-3 Tbsp clear vanilla, depending on your personal taste
2 lbs powdered sugar

(*) A powdered whipped topping mix made by Kraft Foods, usually found in the cake/sugar aisle in the grocery.

Instructions

Theres no wrong way to mix this. I usually mix all but the powdered sugar for a minute or two, then gradually add the sugar, but the only reason I did this was to avoid the sugar-splash factor. The longer the mixer runs, the smoother it gets. Sifting the powdered sugar before blending helps with smoothness but is not necessary.