It sounds like you need separate enrollments- this is not done through Canvas, but through the Registrar of your academic institution. If you reach out to your academic institution, they should be able to create multiple Canvas accounts.
While having a separate log-in to observe each child separately could be a solution, that could be a lot to manage.
I wrote a blog that could be helpful to you: Clarity for Canvas Observers. If you have any follow-up questions about color-coding, nicknaming, or organizing your dashboard, please let me know! Canvas Parent will likely be the best tool for you, as you can look at one student at a time.
You mentioned a toggle, and this idea is open for voting: https://community.canvaslms.com/ideas/8649-parents-toggle-view-between-children?sr=search&searchId=8.... If you have a few minutes to vote and to comment, feedback from observers is always valuable!