Son's Gamertag Changed and He Lost Access to his Minecraft Realm (Nintendo Switch)

...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

Hi Alex,

Thanks for reaching out to us in the forums for this issue with Minecraft Realms on the Nintendo Switch. Based on the message you received, it may be possible that your account doesn't have the correct permissions to access online multiplayer across different
devices.

Is your account a child or adult account? Players under 13 years old will have online multiplayer disabled by default with Minecraft and
won’t be able to join Realms or servers unless a parent changes their account settings.
For help with changing these account settings, you will need to change your
Privacy and Online settings of the Xbox Live account.

For further information on this and other information related to Minecraft Realms or Minecraft on the Nintendo Switch, I recommend the following support articles:

Minecraft Realms

Minecraft for Nintendo Switch FAQ

I hope that this information helps out!

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)?

i help nintendo switch minecraft realm aka.ms/accountsettings

Hi!

Check your Microsoft account privacy settings here: https://account.xbox.com/settings

This article provides the privacy settings required to enable Minecraft multiplayer:

I'm trying to set up an Xbox Live or Microsoft Account (including Realms access for Child Accounts!)

If you’re playing on a Xbox, Sony PlayStation, or Nintendo Switch, you’ll need to make sure you have that console’s online subscription service active. That means you need an active subscription to Xbox Live Gold, PlayStation Plus, or Nintendo Switch Online as needed by your console.

Furthermore, take a look at these similar questions:

• I need help with Minecraft for Nintendo switch realms
  
• there is somthing wrong with my nintendo switch minecraft
  

I hope it helps

Regards