Hi BassMama - things to consider before embarking on modelling:
Does your child take a good picture (Seems obvious but some of the most gorgeous kids just look different in a still pic)
How does your kid act with strangers? Castings can be very quick in-and-out so if your child needs to get used to someone it could be hard
Can you be flexible at short notice? You may get a call at 5pm asking you to go to a casting or shoot the next day.
If your child is school age, how are the school about taking time off?
Don't do it for the money, just look on it as a way to get some different pictures and something for them to look back on, and have some different experiences. You may get many castings before getting an actual job. Castings are either unpaid or a nominal fee of about £15 - you have to make your own travel arrangements. If you get a job, photo work may be from £50 to £90 for a couple of hours work. TV/film/commercials pay more but are harder to get. Again, travelling is not always paid, or may be paid but only from inside the London area (assuming you are looking at London work - don't know the rules re elsewhere)
Not trying to put you off but though this might be useful! My DD is 3, we have had good fun and she has some magazine and book pictures to look back on as well as a fleeting view in a commercial.
Have fun!