I think the difference is imperfect knowledge. The parent doesn't actually know the child is going to mess up, and certainly not necessarily when, or how. I think when there is complete knowledge of the event to be disappointed when it happens is very strange to me.
At the risk of stretching the analogy too far, when we look at real parenting, we see that the parents would punish the child in such a circumstance in order to teach them a lesson and to improve them as people, and help them learn from their mistakes. Eternal punishment does none of these things. Also, we don't punish child 2,3,4 and 5 for something child 1 did. A lot of the things God supposedly does, if we as a parent took the same approach to our children, we would be considered, at best , bad parents, and at worst completely psychotic and evil.
These analogies to me do not translate well where God is concerned, and that is because his behaviour is clearly wrong to us, but Christians are forced to rationalize it as okay because there is no other option to them.
"All of our behavior can be traced to biological events about which we have no conscious knowledge: this has always suggested that free will is an illusion."
- Sam Harris