You can set up a living trust now to benefit both the child and the mother after you are gone, making the mother the trustee.  You can set aside the money, place it in a bank or investment account, and put the account in the name of the trust.  You will have to let the mother know by sending her a copy of the trust document, so it won't be completely anonymous, but your family would not know about it.  The other possibility is to purchase a life insurance policy and make the trust the beneficiary of the policy, with the mother and child the beneficiaries of the trust.