Lots of questions here! I'm also copying your questions into other forums so you can get more answers.
In response to your question about a distance learning Masters, the best thing to do is to contact reputable universities, starting with your country of origin. I don't think being a private tutor will be an obstacle because a Masters is mostly theoretical; there isn't usually a practical teaching element (unless there is a masters I don't know about that involves practical teaching). Given your comment that you regret not doing a CELTA with the practical teaching element, you should think carefully about whether a Masters is the right qualification for you. The UCLES Diploma in EFL might be more suitable but then it wouldn't be easy to do that where you live. International House (London and Hastings) used to do distance learning Diplomas but it was essential to have a tutor who could observe lessons regularly.
As for children's material, I suggest you choose a good course book and just base your lessons around what you find there. As you are new to teaching children, this will be much easier than looking for material for each lesson. For the 7 year olds, take a look at I-Spy by OUP. The material in there is excellent and very memorable for children. The OUP also has a site for teachers and one for students who are using I-Spy. For the 4 year olds, take a look at the Muzzy series. It's a long time since I used it and I can't remember whether it's suitable for that age group. If you search on internet, you'll find some information and reviews of the material.
For suitable books for Cambridge exams, it would be a good idea to specify which exams you're talking about. This means you'll get a more specific answer from our members.