This is one of my favorite past roundups of DIY gifts. You could make these for your kids or have them help you make them.
I recently found this post with 101 DIY gifts for kids.
You could make them this LEGO Pencil Holder with new colored pencils, art supplies, and paper! - from Handmade Charlotte
Kids could make their own snowglobes and you could insert giftcards inside!
Make a LEGO tray (kids can decorate) with a new set - from Somewhat Simple
And I still love this DIY balance board from Elsie Marley
For the younger kids with design oriented parents these hand painted Geo blocks are gorgeous - from Ambrosia Creative
Here's a fun (and messy) project the kids can really get into - from Heart and Habit