Kanopy Kids is a great source for unlimited children's streaming video with age-appropriate content through an adult account.
Kanopy is not available for library cards issued as Children or Student card types. However, an adult can sign up for an account and then switch the device to Kanopy Kids mode. In Kanopy Kids mode, age-appropriate content is presented, content is unlimited, and plays don't county against Adult viewing credits. (Normally the library would be charged $5 when a kid starts watching something, but Kanopy has made this a free feature until April 16th due to the COVID-19 crisis).
We recommend that an adult turning Kanopy Kids over to a child use the Parental Controls feature detailed in the link in order to prevent the child from leaving Kids mode.