This is a great option for short term volunteers. Fort Kochi city is gorgeous, safe and really welcoming. There are loads of lovely restaurants, shops and markets so it is a nice place to explore when you are not with the school. Rainbow will organise great tours for you on your weekends off.
My homestay was really great, the family made me really welcome and they added to the fun and authenticity of the whole experience.
My volunteering experience was mostly with children in the school, and also with teacher some of the mum's English. They were wonderful people, I really enjoyed it. I had no previous experience of volunteering or teaching, I think if you have experience it is better for the children of course - but the most important think is to be enthusiastic, flexible and caring towards your young charges!
I would recommend Rainbow Volunteers to people who want to add on some volunteer experience to their trip to India. Or if you haven't been to India, it is a very good place to start.