Hi Can I put my child for coaching classes for IIT after she completes her 8th std?

If your child is not able to study further in basic language and your child is intrested in technical or vocational courses you can go ahead. but if your child is good in vocational courses there is a vocational stream at class 11th and 12th standard and after that polytechnic is also good. You can

Many coachig institute starts the batch for 9th std student. Do the reserch and then select the best coachig in your area.

That will be quite burdensome and total waste for the child. Put her to coaching classes only after 10th standard, otherwise her divided attention may also spoil her 10th class results.