Paul did what a lot of Christians do; he thought being a Christian meant he could keep the law and he failed miserably. The law will kill you not save you.
Simple.
Paul was alive in Christ and then allowed the law to dictate his walk, placing himself prime for falling with every other step. As Christians, our walk, our perspective and expectations must all be grounded in faith in the person and work of Jesus Christ, not in keeping commandments or...
I'm pretty sure God knew what that heinous culture would make of those children and infants and it was better for the infant to be with the LORD than in the hands of wickedness.