There are some great clips out there which explain the importance of Zam Zam water, the story of Prophet Ibrahim and Bibi Hajar, and how Prophet Ibrahim and Prophet Ismail build the Kaaba back up again.
These will help children get more of an understanding of the philosophies of much of what we do in the Umrah rites, Inshallah!
Here they are:
Story of how Bibi Hajar came to be in Makkah and the well of Zam Zam: https://www.youtube.com/watch?v=QrxCVfDTE2U
Another cartoon on Zam Zam water: https://www.youtube.com/watch?v=AzHX8SlJkoM
The building of the Kaaba: https://www.youtube.com/watch?v=EuPHP9rHYTg