He sleeps really well on the whole. Goes down in his cot at 8pm and sleep through until around 2-3am. He wakes up and usually has around 6-8oz of milk......BUT he then stays awake for around 2hrs. We've tried staying upstairs with him (in a darkened room with no talking/interesting interaction with him) when giving him his milk - but he just won't settle down and wants to play. So DH always ends up going downstairs with him and having to entertain him for 2hrs (sometimes more!). He then settles back into his cot quite happily for another 2-4hrs sleep.
How can we encourage him to go back to sleep quicker??