Your child has fallen off his bike again (it could have something to do with that homemade ramp he and his friends constructed in the driveway). He has a cut on his knee that is bleeding and in need of attention, so why not teach him what to do to stop the flow of blood.
The first thing he should do, after washing his hands, is to remove any obvious debris in the wound. Once this is done, he can get to work to stop the bleeding. The body has an amazing way of protecting itself from losing too much blood. If the blood is slowed down, it will eventually ‘clot’, which acts as a sort of ‘plug’ to fully stop the blood flow and start the healing process.
The best way to slow down the flow of blood is by using gauze or a terrycloth towel to apply steady and direct pressure to the wound for approximately 10-15 minutes. Be careful not to pull off the gauze or towel before bleeding has fully stopped, as this can trigger the flow of blood again.
When possible, applying pressure while elevating the abrasion (i.e. holding it above heart level to take advantage of gravity and slow down the flow of blood) can also help stop the bleeding. To further slow down the flow of blood, try applying pressure to various ‘pressure points’, as outlined in this article http://firstaid.about.com/od/bleedingcontrol/ss/bleedingsteps_3.htm (note: this technique is likely too advanced for children, but I thought some parents might be interested).
Your son may wish to put a Band-Aid on the abrasion to protect the wound from dirt, germs and other things that may cause it to become infected. However, very soon, a scab will form over the wound to protect it, as well as the new skin growing underneath, and a band-aid may no longer be necessary. He should try his best to avoid picking off the scab (having said that, this seems to require an almost-Herculean effort for kids), as this may lead to a longer healing time, or a scar. Simply let the scab fall off on its own, once the new skin is ready.
For more detailed information about the clotting process, as well as additional steps that can be taken to look after minor cuts and scrapes, check out the following resources (note: these sites were also instrumental in the writing of this post).