For kindergarten level, I suggest to start with pictures to teach simple words like "apple", etc. You should perhaps also start with some phonics introducing lettersk, combination of letters, and finally entire simple English words.

I cannot make any suggestions for the other levels you have mentioned, but here I would use songs and language games. Children at that age are great in imitating what you show them. Make use of their curiosity and their willingness to learn new things!

Good luck!