How can I buy tickets for children under 1.2 meter in discount?

You could book the tickets through TravelChinaGuide and tell them your kids are children under 1.2 meter. They will book it for you. By the way, I ued to be told that kids lower than 120cm could take railway trip for free In china, however, who will have to share the seat/berth with his/her parent. If your kid would like to have a seat/berth, you could buy a child ticket for him/her.