Besides PicMonkey, there's also PiZap, a photos editing and collage maker.
I created this photo by selecting a background and then I selected cut-out and painted the kids, so they would be added to the background. I also added the doggie.
It's FREE and it has many options. Adding a frame, backgrounds, Timeline covers for Facebook, plus photo editing.
This photo, I added the frame and text.
Below is the template to make a collage.
Choose whatever one you want and start adding your photos.