Statutory Doents required for opening children (1-6 Yrs) day care centre. Any exemption from Karnataka Govt?

You need to registration with Registrar of Societies, Chit Fund and Firms under Soceities Registration Act 1860. Since your work seems charitable this registration will apply. In case you want to start this venture on non charitable basis, then there is no need for registration. Having a PAN is sufficiant for you.