can you recover deleted realm worlds on the nintendo switch?

Hello Billy, this is Manuela. I'm an Independent Advisor and community user like you, ready to assist with this.
Not a Microsoft employee.

I would like to let you know that, as far as I know, it is not possible to recover a deleted realm if you didn't make a backup

...we have now started fresh with a new world in minecraft on the ipad. However, i still cannot access this new world on the nintendo switch minecraft

Minecraft doesn't store the worlds "in the cloud" so that multiple devices can access one world.

If you have a world stored on your iPad, the Switch will NOT automatically have the world, even if you use the same Microsoft Account.

Your son can either "visit" the world on the iPad with the Switch, while the iPad is running Minecraft at that time through Multiplayer.

If you really want to have the world shared across both devices, your only option is to "rent" a realm that you have to pay for in monthly subscription fees.

Or if your son is okay with transferring the world from one device (e.g. iPad to the Switch and only play on the Switch from then on), you could use a free trial for Realms to transfer the world over.

To do that, your son activates a Realm subscription with a free trial on iOS, and uploads the desired world to the Realm service.

Then he connects the Switch to the same Realm, and downloads the world to his Switch.

Then you cancel the Realm subscription via
https://my.minecraft.net/profile/realms

Once you delete a saved world there is no way of getting it back. Anyway try with Mojang support if they can help you.

Have you an active Nintendo Switch Online Subscription? I ask this because I found the following Q/A on Minecraft Nintendo Switch FAQ:

Can I play Realms on this edition?

Yes, Realms is available on the Bedrock edition of Minecraft for Nintendo Switch. To play online on a Nintendo Switch, you need to have a Nintendo Switch Online subscription, so this is a requirement for playing on Realms. More information about Nintendo Switch Online can be found here.

Furthermore, can you post the entire error message (better a screenshot/photo)?

Also, just a reminder that to play online on a Nintendo Switch, you must have a Nintendo Switch Online subscription. So this is a requirement for playing on Realms.