what are some ideas for decorating the inside of my house for christmas?

This is the perfect opportunity to make special crafts with them to put on the tree and around the house.
Children of this age love pictures. Have them select photos from magazines that they like, which could range from nature scenery to animals to toys. Have small pieces of cardboard precut in the size and shape of the ornament with a hole punched in the top. When they select the pictures, you can cut them to fit the precut cardboard, and then let them glue the pictures to the cardboard. Allowing them to place them in any way they like on the cardboard, whehter its crooked,, crumpled, sideways,etc. If you use school craft glue the color of the ink should not run and the photos will stick easily to the cardboard. Once the ornament is dry, you can run a ribbon through the hole in the ornament to hang in the tree. In this way there are not sharp metal hooks.

I hang pre-lit garlands in the door ways and on the entertainment center, I have a ceramic village that I light up (but it's houses from the dollar store, not $20+ houses), I have a christmas village display my mom and I made years ago, a gingerbread house that my son and I made (which is something you can get for $10 or less and do with the kids) and various decorations we've gotten over the years from a musical snowglobe that sprays snow, a red and green basket filled with candy canes, and other knick knacks I got when I was an Avon rep, a ceramic tree I made as a teenager at my community center.

But you can make construction paper chains with the kids, paper snowflakes, and other crafts like that for now that involves them without breaking the budget

My daughter will be 4 on the 1st, and we have already made cut out snowflakes out of paper plates, and then decorated them with smashed up fruit loops and glue! We then hung them up in all of our windows, it's very pretty, and very cheap! Another thing you can do is use cardboard and cut out circles, then glue them together to make a snowman, then if you have old x-mas cards cut them into all kinds of pieces and have your children decorate their "snowmen" with the cut outs! Another one we are going to be doing tomorrow is making applesauce cinnamon ornaments, very easy and inexpensive as well, all you need is applesauce and cinnamon! You can look up the recipe online!! There is soo many fun crafts to do and very cheap ones at that, just look it up online! Have fun being festive!

Go to Michael's Craft store if you have one near you. I just went there today and for $15 or so I bought 2 packs of wooden ornaments that came with markers and glitter glue. There were 6 ornaments total and they are cute. Then I also bought 3 thick wood ornaments in the shape of a christmas tree, a stocking, and a star. Let the kids paint them in any way they like, then take a paint brush and brush a coat of glitter glue over the top. You can make a nice wreath pretty inexpensively. Buy a real or fake wreath, and make applesauce cookie dough ornaments (I have recipe if you want) and let the kids pick out cookie cutter shapes to cut the dough into. They bake up super super hard. The kids can paint them with glitter glue and then you super glue them to the wreath. Michaels has the 2" wide Christmas ribbon for pretty cheap too, and you can wind that in between the ornaments. Bowls of peppermints or candy canes are good too.

Inexpensive light strings around the windows. Buy the really small wall mount things by I think it's Mead or Command one of those 2. They are so much better than using nails to hold up the light strands. Also, draping colorful garland over ANYTHING makes it pretty to a kid. i have a prelit village thing that is all one piece, about 2.5' long, and it sits on a shelf. The kids love that. Gingerbread houses are another thing that is easy and fun. Make it more about spending time with them, letting them create things, than about having a perfectly beautiful decorated house, and both you and they will love it all the more.

I love homemade items - strung popcorn with cranberries (if they are affordable), paper chains that can be added to daily, ornaments made from popsicle sticks, clothespins, pre-cut craft foam, and little doo-dads that they can get creative with, making tassel dolls from yarn, drawing large pictures and coloring them with bright colors so they can be cut out and hung in the windows and on the fridge.....lots of things.
You can also go outdoors and gather up decorative sticks and twigs to glue around picture frames made from popsicle sticks. Go to a Christmas tree farm or seller to purchase scraps of pine to make your own wreath or garland or to place around the home for the scent - sometimes they will let you collect what is on the ground for free.
Have fun!