Hi, what is the fare for children using airport express train in Beijing?

A child shorter than 4.3 feet (1.3 meter) can ride free, but he/she must be accompanied by an adult. When an adult travels with two or more children less than 4.3 feet, one of the children can ride free, and the others pay full price of CNY 25. Children taller than 4.3 feet pay full price. :)