NC Family

I currently use Mac's Parental Controls feature to limit the amount of time my child can spend on the family iMac on a given day. For instance, once he's done with homework and chores, he's allowed to login and use up his weekday allotment. Sometimes I want to grant him extra time as a reward for something, yet the iMac is often a good distance from where I situated in the house. I'm looking for a way to "extend" my child's time using an iPhone app for remote control so that I don't need to go to the Mac and type in my admin username and pw. Ideally I would also be able to just lock/unlock his iMac screen using my iPhone from anywhere (over internet) at any time. Will Alfred work for this? Any other suggestions? I've been web searching like crazy, reading about different software offerings, and cannot seem to come up with anything like this. One would think Apple would supply native remote control capabilities across its product line-up. Thanks in advance!