Like lambs, children are helpless before the world. Lambs and sheep are a picture of helplessness. In the real world of Judea where shepherds had flocks and tended them, Peter and the disciples knew how vulnerable were those sheep if the shepherd didn't care for them. In the same way, God's people, and especially the children among us, are subject to the world of evil and danger around them. Satan doesn't wait until the children are adults to test them and destroy them.
Children are subject to danger.
One of those dangers threatens them even before they are born. I am speaking of abortion. Since 1973 there have been over 35 million abortions. Children's mothers are also subject to danger. When I ran across a description of a mid-pregnancy abortion, I was horrified at the description of the syringe jerking against the mother's abdomen as her child went through his death throes.