If you want to keep the grass down, get a couple of geese.
If you buy goats you have to be really committed to them - remember that you will have to register your premises with DEFRA, keep a movement book, worm them, vaccinate the, cut their hooves, muck them out, milk them twice a day every day (no days off and it is very very hard to get someone else to milk them), feed them, etc etc.
And they still won't keep the grass down as they don't like eating things that they have trodden on. They need to have constant access to shelter, and a shed to sleep in at night.
If I haven't put you off enough, then contact the British Goat Society, and ask them to put you in contact with your local goat club. Someone would then be able to teach you to do all the things you need to be able to do.
My parents had goats for 25 years or so - over that time Dad was called in by the vets to go and sort a lot of people out who thought goats were a good idea and didn't know what to do
If you don't want milk, Pygmy goats are a good option though - get a neutered male and they do make good pets and are a nice size for children. We had a rescue one for some time, and he was my responsibility, as opposed to the Saanens who were dads (but I still had jobs to do for them)