I live in the US, but I’ve had a fair amount of experience with foreign students in private schools. I’m also not sure if this is a government or private school that your child would be going into in India. Many schools overseas are a year ahead of their public counterparts in the US, so before the student is admitted he would need to take an entrance exam so the administration would know where to place him and how well he would fit in with their academic coursework.
If he’s not fluent in the language, it gets much more complicated, but not impossible. I looked up the CBSE school system (the link I found was for high school), but I’m not sure if the coursework in your school is taught in English or not. .
Entering school in the middle of the school year in India makes things more complicated, just like it is here in the US, but schools anywhere are rather used to these sort of transfers. It would be helpful I’m sure, if he could start at the end of a break, so he could begin the coursework with all the other children.