Can I convert a MacBook air administrator account to a parental control account

Caution: DO NOT try to change the names of ANY accounts. Create new accounts instead.

The existing Admin account can be used to add additional Administrator account(s). You MUST have at least one, and you MUST remember the password or write it down. Losing it is a MAJOR disaster.

Once you have another Admin, you can log in as the new Admin and demote your child's account to a "regular" account. They lose nothing in that account except the ability to install more stuff. And then if you wish you can put parental controls on that regular account.

You expressed concern about losing their stuff.

¿what is the date of your most recent backup?

-- If never, post back for additional steps to take.

When my kids were growing up and the Internet was fairly new, I made it clear that their use would sunset on schooldays at a certain time of day. Then I used the tools available to make it so. (now Parental Controls can do similar tricks and more).

If they wanted additional time, they had to ask me to extend their Internet time. The thought process was to encourage them to budget their time to finish their real work before their Internet died, and not to waste time they might need online for homework, unless they were all caught up. To try to teach them to self-regulate.

My older son ran out of time only occasionally. He worked hard and did not goof off, he just had a LOT of work. My younger son never ran out of time. I think that setup worked well, and did tend to teach what I wanted.