The number of pages in abook for children should be different than the adult one. It also depends that
how much is your book interesting for children. Usually children get bore soon
and they want to read new things. So it is really a good idea to keep the page
numbers into the range of 34 but if you exceed it to 50 then it is still fine.
Be careful with your content. Increase the quality of content so it will allow
you to increase the number of pages.