Also keep in mind that many children have the attention span of a gnat....for weeks or months they want to ride then they don't. As they grow they develop other hobbies, friends, likes, etc. If you feel you have to have a foal for him to learn on or to bond with, go buy one that needs a good home. That way you won't be bringing yet another equine into the world, you will be helping one and all will be well.
Breeding is a crap shoot and as FeatheredFeet said, there has been a larger number than not of lost or aborted foals and or the dam dying as well. At the age of this mare you are possibly going to get, you will need to do a full health check, uterine check, all sorts of fun stuff that will run you into money.