If you want to explain it to them by showing some animated video, you could show your children this video:

https://www.youtube.com/watch?v=sDlvnR3qxnk

If your children are already able to read, you could also print this sheet to help them understand COVID-19:

[https://www.drk.de/fileadmin/user_upload/Coronavirus/AKS_I2_Corona_fuer_Kinder_erklaert.pdf](https://s3-us-west-2.amazonaws.com/secure.notion-static.com/e80defd9-8f3f-4aad-a105-649aceea6674/AKS_I2_Corona_fuer_Kinder_erklaert.pdf)

https://www.drk.de/fileadmin/user_upload/Coronavirus/AKS_I2_Corona_fuer_Kinder_erklaert.pdf