I wonder if the parental controls are found on the USB setup flash drive. I don't know if the drive application is the same for both the 3825 and the CGN3 but the drive for the CGN3 has parental controls. The CGN3 has device management built in, but I don't know if it equates to the same management capability as found on the USB setup drive. Having said that, I would recommend throwing out the drive and never using it, same recommendation as the tech support individual I was speaking to after I experimented with the drive application. Following said experiment, I ended up returning the CGN3 as it partly bricked the CGN3. So, good idea, no cigar.
Yep, best bet is to bite the bullet and buy your own router, which will give you much better control capability over the features you are looking for. The additional security benefit is that you can probably run your entire home network behind that router, completely isolating it from the Rogers equipment, and you will have much better wifi performance as well.