my main advice is be prepared for drama! i was babysitting a child years back and his mom kept telling all her friends about me, so before you knew it i had 4 one year olds. it was DRAMA. get a contract and stick to it! i tried so hard to be nice and all it did was get me walked all over. it seemed like every week someone was drastically late picking their kid up, or had an unexpected bill and was paying me late, or dropping their kid off 2 hours early, or not bringing diapers so i had to use all of mine, not packing a change of clothes so i was sending them home in my daughters and not getting them back. it was a mess. i could never do it again. i just dont have enough of a spine to stand up to people like that.
Unfortunately, you would HAVE to get licensed too, because you get one set of parents like that and when you tell them you cant watch their kids anymore they turn you in to the state and you get fined. Luckily, getting licensed is relatively easy.
if you are looking for back-up income, try going to http://www.PerfectWorkForMoms.com it isnt a get rich quick thing by any means, but it would help you have a little extra for back-up.