The vapouriser keeps moisture in the air - so as long as you don't position it right next to the cot - any age should be fine - if they are older though yeah a bit closer. And if for younger bub leave the door open all the way instead pulled to a it to keep it all in.

In canberra it can get very cold at night and I find vapouriser wonderful for keeping the chill of the air in my daughters room instead of leaving heaters on, or using portable fin ones etc. we just turn it on around 10pm before we go to bed. Not evey night of course, but when I can tell she is getting sniffly or has a night cough.

I have bad sinuses with preg especially and have been using it myself in my room the last week - OMG what a difference it has made to my sleep as well.

go for it I say! It is just steam.