How about large international travel posters? They can be bought online, tend to be colorful and the frames are very inexpensive. In addition it will teach your children about other places in the world.

Have your kids paint clothes pin then string the clothes pins on ribbon hang the ribbon on the wall. It’s perfect for kids artwork. Makes decorating for parties and holidays super easy as well. Later on you could get a few big wall stickers of a trees and place them so it looks like your pictures are hanging from the trees.

Do something big and colorful. I like the idea of using kid's work.

I would work with the furniture a little to try to get it facing the wall where you want to hang art...i might also say the kid idea is cute while they are small or if one or two are talented ...even to the point of adding a space for them to create their masterpieces...but if you ever want to use this as an adult space...like for Super Bowl ,etc...the art should be presented in a little more adult way...framed in plain black frames?..in groupings under the artists name? With little easels ...til they outgrow it...

It does seem like the couch should be a little more parallel to the tv..