Answer
There is much difference between the sudden death of infants and that of grown persons. The latter may have much work to do — many sins actually to repent of, and many evidences of their interest in Christ to examine and establish — in order to a more comfortable death. And so sudden death may rightly be dreaded by them.
But the case of infants who do not yet exercise their reason is far different. They have no such work to do, but are purely passive. All that is done in order to their salvation is done by God immediately upon them. And so it comes to the same thing whether their death be more quick or more slow.