I used to get nosebleeds almost every day during the summer when I was younger (up to about the age of 11) and fairly often during the winter. On a bad day in the summer I'd have ten. I had my nose cauterised twice using silver nitrate - it tingled but didn't hurt. Didn't really work though.
I used to get them more on days with high atmospheric pressure - more often during the summer, but sometimes this happens in the winter.
Never make a child with a nosebleed (or an adult for that matter!) tilt their head back. I found the best thing was squeezing the bridge of my nose and applying cold (ice or cold water) to the bridge of my nose and the back of my neck (seemed to cool me down enough for the bleeding to stop). Sometimes they'd be so bad that I would choke on congealing blood even though I was leaning forwards - the last one I had was a couple of years ago and I nearly went to hospital as it wouldn't stop and I was having trouble breathing.
My MIL swears blind that squeezing your nostrils together is the way to stop a nosebleed, but I found that it just meant it all clotted together and started to bleed again when I let go when I tried this (long before I had a MIL too!).
To return to the point of the original post (), I used to also get nosebleeds at night around the time of a cold - I think when you have a cold, your nose can be quite itchy, so rubbing it or blowing it may trigger a nosebleed.
One last thing, people also told me not to blow my nose when I had a nosebleed, but I found that giving it a good blow often got rid of the 'plug' of blood and allowed it to clot properly and more comfortably.
I'm gonna gt a nosebleed tomorrow, aren't I?!
Ooh, just thought of another thing - bambi06, you say that your DS has had them two nights running - again, not uncommon IME - once you've had one, the blood vessels in your nose need time to heal and one good rub of the nose can cause another bleed easily. Hope your DS is OK tonight - I remember all too well the tickly sensation of a nosebleed starting just as I lay down to go to sleep and knowing I'd have to get up to deal with it (I was a bit older than your DS by the sound of it when I remember this though!).
I'm going to stop writing about noses now