It is a common misunderstanding, that keeping the our photos in iCloud is like storing them on external drive, as a backup, independent of our other devices. But iCloud Photos is primarily a syncing service, designed to keep the Photos Libraries identically and in perfect sync on all our devices. if we import new photos on one of our devices, they will appear on all our other devices, and when we delete photos from one of our devices, they are deleted everywhere. So, when you deleted your Photos from the iPad, while it has been syncing with iCloud Photos, you deleted them from iCloud and all devices that have been syncing with iCloud Photos. I take it, you have checked the recently Deleted album? It is your only safety line to recover deleted. items. Once they are gone from Recently Deleted, they are deleted permanently. That is why it is essential to make regular backups of our iCloud Data. Apple is storing them safely, but only saving the current state. We can restore a new device the current state, when our devices is lost or stolen, but iCloud Photos cannot be used as an archival backup to protect us from user errors, because the previous state is not saved. For this, we need to keep a separate archive, for example, an archive on our computer or make vbackups with Time Machine.
If you do not have any backup, Mima, stop using your iPad at once. There may be traces of the photos you have downloaded still in the in the storage, where they have been and data recovery software might be able to find them.. But when you keep using the iPad these traces will be overwritten by new data and will be lost. It is essential to to use data recovery as soon as possible. And only the local copies on the iPhone or iPad can be recovered, not the the items that are only on Apple's servers.
Data recovery software is expensive and the result is uncertain. Try recovery software that is coming with a trial version, where you can see what can be recovered, before you have to pay. For example, if you have a computer, you could try Disk Drill to scan the iPad or your iPhone for traces of your photos: https://www.cleverfiles.com/de/lp/data-recovery-software.html