No, we should not murder babies so they can go to heaven because first of all, God says do not murder. To do so would be equivalent to doing evil in order to do good and to set one option against another in order to try to do what is good. This is the error of the end justifies the means. We are not supposed to set a possibility that all babies go to heaven against the clear teaching of God not to murder.
Second, we don't know if all babies go to heaven. Though we might believe they do (as I do), believing it doesn't make it so. Therefore, an opinion is not sufficient grounds from which to justify murdering babies--that is also obviously a contradiction to God's word and should not be done.
Some say that it is okay to murder a baby as long as he/she repents later. That way, the baby goes to heaven; and the person is forgiven. But, this horrible reasoning completely fails to recognize that those who are truly Christians do not purposely sin so that they can be forgiven.
Rom. 6:1-2, "What shall we say then? Are we to continue in sin that grace might increase? 2 May it never be! How shall we who died to sin still live in it?"
The thinking of unbelievers who try and refute God's word by encouraging people to murder so that people can go to heaven is a sign of their profound sin and blindness.