My children have just returned home from a weekend with their dad. DD (4) was half asleep as she walked through the door. DS (6) was wide awake and buzzing. Normally he's in bed by half six and asleep by 7 at the weekend. I've just found out that he had spent the hour long journey playing DS in the back of the car. This bothers me on 2 levels - one, it's too stimulating for him so near to bed time and two, surely it can't be good for his eyesight in the back of a dark car. Am I being unreasonable?