We spent 3 months in India when our oldest was 18 months. It was an adventure for sure. We travelled around the south, particularly in Kerala, which was lovely. We spent some time in Bangalore, Pulinkudy (tiny village), Cochin, and went up to Munnar and the hillstations, checking out both the tea and spice plantations.
In addition to TB and the usual travel vaccines, you need malaria profylactics. Our son lost his apetite, as this was a side effect of the antimalarial drugs, and hardly ate for three months. He also had a viral fever at some point, which was pretty scary. His health was the reason we only stayed 4 months, rather than 6 months as we had planned. He was so young, it only took 4 months of no apetite, for him to develop severe iron deficient aenemia. This was not diagnosed until he was nearly 3.
I think I have seen the inside of 5/6 different hospitals during our stay, and I was really impressed with the medical care we received. I had food poisoning 3 times, despite being very careful. I mostly stuck to a vegetarian diet, and I got ill on each occasion I ventured beyond veg to try the chicken. A shame, as I love indian food. Keralan vegetable Pakora is the best!
In Munnar, our son was so ill, he was barely conscious. The entire village turned up (it seemed to me) to gawp at this pale sick extremely blonde little child, and prod him, and giggle at me, sitting with him lifeless in my arms on the bench outside the hospital, waiting for test results. Some women tried striking up conversations with me, asking if I was sri lankan. It was quite an experience. It was new years eve, and almost like a miracle, after having been out of it for more than 24 hours, he woke up as the fireworks started, looked at the orange at the bedside table, whispering "food". So we took him outside to look at the fireworks, and the next day he was already better.
Make sure you have adequate travel insurance. Not that it really matters, day to day you still have to pay in hospitals and for medicine, but if something out of the ordinary happens, it is good to have the security of proper cover.
One of the most memorable experiences was a backwater cruise from Cochin to .... boy I cant remember. 24 hours, just us, our boatsman and the chef.
One tip: buy moscito repellent locally, there are some fab brands out there, and bring your own insect net, and always bring with you longsleeved light shirts and trousers for wearing after dark. The mozzies are very intrusive.