I think you have had some GREAT feedback from everyone here!
It is wonderful to dream, but to make those dreams come true, takes LOTS of hard work and dedication!
To be a good photographer has little to do with the gear (a couple of people will disagree with me, but I believe that most will agree)! I have seen some AWESOME photos taken with a Rebel XT and some really crappy ones with a 5D MarkII and yet everyone will agree that the 5D is a much better camera than the XT.
I recommend you get a "lower end" camera and only upgrade once you "rock" it! I would invest in a better lens if I were you. I love the 50mm 1.4 (I hated the 50mm 1.8 - my copy was honestly hit or miss on focus). The 50mm is a fixed focal (it doesn't zoom) and I also have a Tamron 28 - 75mm 2.8, but I rarely use it when shooting kids.
A good book to start out with is Understanding Exposure by Bryan Peterson. And MLKStudios has a really good on-line course.
Something else you haven't mentioned is buying a post processing programme. Something like Photoshop. You will also need to decide which version you want. BUT my personal recommendation is not to do ANYTHING in Photoshop until you can get it right in camera. Too many start-out photographers take bad photos and try and fix them in PS. Learning to do post processing that is "clean" is actually much harder to learn than people think. You will probably also need to get a calibration programme for you computer to ensure that what you see is actually they real thing (like colour casts, the right skin tones etc etc. etc.)
There are many children's "photographers" who honestly just suck! They got a DSLR camera for Christmas and their friends and family told them their photos are wonderful and suddenly they are photographers! Truth is that they charge seriously low prices and if they had to really work out their pricing they would find that the value they put on their time is probably a negative figure!
So, one could choose to go that route, or you can take the time and put in the effort to learn (not only the photography side, but also the business side) and charge what your time and talent is really worth!
I think (personally) that a good time line could well be between 1 to 2 years before you are really ready to break into the market and make a success of it! And that is if you really work at it and apply yourself!
Kudos to you for asking and finding out before buying the camera! Good luck with your venture!
HTH
Anelle