they are a couple of religious idiots, it was their third child (woman pregnant with a 4th when arrested)
and they lived by the doctrine that "The righteous shall live by faith. It’s God who is sovereign over disease and those sorts of things and, of course, ultimately deaths."
so they raised their kids without any medical assistance, so when their third kid got sick and didn't eat or drink, they just put her to bed, God will provide for the 10 month old during the night, except, starved, dehydrated and sick, she died alone in her crib, God's will
turns out the law doesn't see it like that and they both face charges of felony murder and first-degree child abuse