Hi Kristen,
well, you're opening a can of worms with that one hee hee.
Most of the time if you are going to report taxes they will want a higher wage because they will have to pay taxes on what they earn. However, it's illegal to pay someone and not report it to the IRS. I am pretty strict about most things. This and taking my own candy into the movies are 2 places I am just willy-nilly about not following the 'rules'.
If you report taxes, then you should also research insurance (what happens if she falls down your stairs while caring for your son?) etc. If they make above a certain amount for the year you will have to withhold and file FICO and, in addition, there are decisions you will have to make about if she is an independent contractor or an employee (which has to do with set hours and how much direction you give her about 'how' she does her job- so you should look this up).
Here is some information
http://www.irs.gov/newsroom/article/0,,id=106189,00.html
Now that I read this..... it says that you can claim an exemption of up to 3000 if you are single or 6000 for both spouses who work. that's a credit - not the amount you will get back. So, depending on your income level and where you fall in the tax bracket it may not even affect the tax you owe. I would have them figure the tax credit this year and see if it would help you or hurt you to claim it.
Just my $0.02
B.