Train ticket-- Beijing to Suzhou

We are a family of 5 ,with 2 children aged 8 and 9 ( both under 1.5 m in height ). Do children pay full price or discounted? We are thinking of buying soft sleeper for an overnight ride. Can the 2 children share one bed so that all 5 people can stay in one unit / compartment ? If so, how much do the children pay? Thanks