I've been having this same issue for the past couple months. I've disabled parental controls several times and it seems the settings don't stick. (I don't know how they got enabled in the first place because I never did it originally.) There has to be some way to keep the parental controls disabled.
I'm using Google Chrome and logged into the primary account when I try to change them.
ETA: I just had the same thing happen literally less than five minutes after disabling the settings and watching one short video. This is getting very annoying.