I have children 3years and 9 years. What is the fare policy for train tickets?

Children under 1.2 meters (3.9 feet) and accompanied by adults travel for free; Children between 1.2 meters and 1.5 meters enjoy the child ticket discount: the price of child ticket for hard/soft seat is half of the full price; the fare of hard/soft sleeper is still half of the hard/soft seat if the child shares a bed with the parent, and it is 75% of the full fare if the child requires his or her own bed.

i found the above information at the following page, where you can find the detailed notes about child ticket:
https://www.travelchinaguide.com/china-trains/tickets.htm