First, it’s important to notice that even if there were nothing wrong with the analogy, the argument still wouldn’t work, given that cognitive development is not necessarily the same thing as resourcefulness and creativity. In general, the flaws that the LSAT is asking you to find occur closer to the main conclusion. So, in this stimulus, there may be a flaw with the analogy, but then there’s also a flaw in the connection between the analogy and the main conclusion. Usually they’ll be asking about the latter rather than the former, but I don’t think it’s bad that you picked up on the fact that the analogy may be flawed. Notice, though, that D doesn’t actually pick out a flaw with the analogy- rather, the flaw would be that there is some sort of relevant difference between raising children and writing a good novel.
Again, I don’t think it’s bad that you identified a flaw in the analogy- that’s a sign that you’re being super critical when reading these arguments, which is really good! But there are tons of stimuli on the LSAT that make the same basic flaw as what happens in this stimulus- the conclusion uses one term, and then the premise discusses something closely related, but not quite the same thing. In this case, the conclusion involves the term ‘cognitive development’ whereas the premise discusses being ‘creative and resourceful’. This kind of thing happens all the time on these questions- the more you notice it when it happens, the better prepared you’ll be.