I thought this one looked really fun for kids but there are a lot of great ideas on Pinterest. Good luck! https://www.trendyhomedecorations.com/diy-a-childs-desk-in-wood-and-copper/
Here's a picture of a desk made from an old crib! So cute!
ezpz! So many options for you. You can attach boards to the wall at the proper height and use an interior door without the hole for the knob, along with with 2 front legs. This can then be adjusted over time as they grow.