i already have an ipad, just bought an iphone, do I need 2 apple ids?

You can use the same Apple ID, but their data will sync to each others devices if they use iCloud. You should use separate IDs if they want separate data on their devices. If you do use 2 IDs, set up Family Sharing so they can share purchases.

Family Sharing

Family Sharing - Set up

It is almost always preferable for each person to have their own Apple ID and also it is almost always a bad idea for a person to have more than one Apple ID.