Hi, Suzanne, welcome to iPF!
If you enabled PhotoStream just recently, this is the reason why the pictures don't appear on your iPad's Photos app. PhotoStream starts syncing images that were added after it was enabled.
If your problem is different from what I'm assuming, please add a bit more information:
Is your iPad up to date? The latest software for iPads from 2 onwards is 8.2. What did you try to get the feature working?