I need to install parental controls on my kids's MacBook

..Perhaps you may wish to study Family Sharing, to

what's involved; and set up an account for a child..

• What is Family Sharing? - Apple Support

https://support.apple.com/en-us/HT201060

"Parents can create Apple IDs for kids under 13* in their family. With an

Apple ID, a child can use their own account on their own device — and

even make their own purchasing decisions. But with integrated parental

control features, parents can still set limits."

• Set up Family Sharing - Apple Support

https://support.apple.com/en-us/HT201088

"Family Sharing makes it easy for up to six family members to share

App Store purchases, Apple subscriptions, an iCloud storage plan, and

more—all without sharing an Apple ID. You can set up an Apple ID for

kids, set permissions remotely with Screen Time, and approve spending

and downloads from a parent's device with Ask to Buy. You can also set

up Apple Cash for a child or teen, or set them up with an Apple Watch. 

Learn more about what you can do with Family Sharing."

• Use parental controls on your child's iPhone, iPad, and iPod touch - Apple Support

https://support.apple.com/en-us/HT201304

• Family Sharing and Apple ID for your child - Apple Support

https://support.apple.com/en-us/HT201084

"In macOS Mojave (10.14) and earlier, "Parental Controls" was a separate section under "System Preferences."

https://duckduckgo.com/?q=parental+controls+on+your+childs+mac+computer&t=ffab&ia=web