I became a believer in Jesus as a child. Yet, I was not a baby. A baby is not a child, just as a child is not an adult. What Jesus is speaking of is our attitudes in this scripture. Children believe and accept and so must all who desire salvation. We are saved by faith and our entire walk is by faith.
Babies do not have the ability to comprehend salvation. You have come to a false understanding of what is being spoken of.
"These little ones believe in Me" in Mathew18:6 proves all babies believe in Jesus. The problem is not with God's creation. The problem is with humans who forsake faith in Jesus & choose the forbidden knowledge of good & evil as they grow up.