I have two sons - 3 and 1.4 yrs - and we recently put them in the same room together and it's a nightmare.
It's the youngest son who is the little devil - stands up in his cot yelling and giggling at his older brother, who happily joins in. They are keeping themselves awake until 9:30pm-10pm (and they go to bed around 7:30pm).
It's only been a week, and my DH has told me to give it a bit more time, but is it more sensible to separate them now and try again in a few months' time? Much as I love joyful giggles between my sons, at 9.30pm at night on a school night, it's getting a bit much.