Most of the Stroud area village schools are pretty good and there are children at the Grammar Schools from them all. Minch, Rodborough, Woodchester, Chalford, Thrupp, Kings Stanley, Eastington, Frampton. These are all nice villages, small ish schools with a good sense of community. Of course you will pay more for property in all of these villages. Nailsworth is a bigger school and rapidly improving. That's a nice town.
Much depends on the head teacher.
Best thing to do is read all their prospectuses. Some are church based with a Christian focus, bear this in mind. They have different facilities in terms of space, playgrounds, garden etc. You could start looking at Playgroups, which often feed in to the primary schools. You will be ready for those soon.
The primary schools don't prepare them for the eleven plus exam you will have to help with that, or pay a tutor.