BlocksCAD is an online 3D design tool made especially to teach children how to do 3D design. There are many tutorials for it online. https://www.blockscad3d.com

Structure Sensor is an iPad accessory for 3D scanning. It's pricey, but I've used it and it works well. There are also iPhone apps for 3D scanning, some of which will run on the iPad. I haven't tried any of them. I suspect the results aren't as good as the Structure Sensor, but they are much less expensive. There are reviews of some of them here:
https://all3dp.com/2/5-best-3d-scann...ur-smartphone/