If sales won't go so well, or if you would like to try a different marketing approach, you might consider this: Instead of asking for money upfront, you should give the app for free with a few sample monsters. Then you can provide the full package with in-app purchase. The logic behind it is that it will be easier to convince the parents to pay for it, after their kids love it. Another reason - with a $2.99 price poi…
I am not convinced that kids will nag their parents enough to make them pay to upgrade - I suspect most parents will just be happy to let their kid play with the free version.
Here is a video of my daughter playing the Racing Penguin - http://www.youtube.com/watch?v=qaF6dPiJ-NM
She went through the free version in a zippy and kept playing it over and over again. I took her iPad, disable Restriction and bought the paid version.