Three weeks and more, the child's height is around 100 cm, do I need to buy a child's ticket?

You need to buy a child ticket. Many projects are restricted to children under 90cm. If you are over 90cm, you need to buy a child ticket.
Shanghai Disneyland, on the day of visit, children under 3 years old or 1.0 meters tall and below are admitted free of charge. If it helps you, please click green “Accept”.
No, I hope this helps.