The laptop reappears

Today was a bit of a crappy day, Reuben had a really bad night due to growing pains in his legs and this morning kept falling over, I was zombiefied and Isaac was his usual cheerful self, at least one of us was. We were all so tired that my laptop made a reappearance and Reuben spent about an hour on the reading eggs website. I felt a bit deflated as our tv and computer free days experiment was going very well indeed, on the upside it meant that I managed to do some University work. So what now? I don't want to go back to a computer obsessed child in the house, do I enforce specific times when he can use it? How do I explain it to a free spirited nearly 4 year old? The continuum concept is easier to follow in the jungle I guess...