I would totally suggest you https://sarahbrinson.livejournal.com/431.html because it contains amazing resources that'll help you write, read,  count etc. You can also find basic online courses for kids on platforms like Coursers. They are usually free, and are great!

Flash cards are last season!  What works for me is Fishbone method of learning, you can read more about in case you are interested. It's really well visualized, so it's gonna be perfect for kids. Shortly, this diagram looks like a skeleton of a fish. Fishbone diagrams are typically worked right to left, with each large "bone" of the fish branching out to include smaller bones containing more detail. A lot of people use this method nowadays, and I would recommend to try it out