Jungle, I know exactly how you feel. Although I don't have kids, your situation sounds familiar. I think precisely because we're so effective (the fact that we're communicating on a productivity forum is evidence that that's probably the case) is it the case that we end up being able to goof off a lot while still getting everything done gangbusters. This in turn makes us feel guilty because we think about how much more stuff we would accomplish if we hadn't goofed off at all.

I think the solution shorten the time you give yourself for each or your projects, that way you'll get them don in the same amount of time, but since you won't have time to goof off, you won't. My suggestion is just an application of Parkinson's Law, which states that "work expands so as to fill the time available for its completion." If that's the case, shorten the time alloted to a project and I'm sure it will result in you still doing a bang-up job, but without the goofing off. Take the time you save and schedule it for guilt-free goofing off. If you have good systems, then the status of your projects shouldn't creep into your head during goof-off time.