My brother did this, he decided to become a stay at home dad, partially because he made less money than his wife.
From what I have seen, he talked to some existing clients that needed tweaks but didn't want to keep contracts with the company he worked for and he essentially poached them. He also leveraged people he knew, like graphics artists etc for more leads. Essentially a trade, they refer to each other.
Overall he works about 15 hours a week, when the kids are in school and delivers projects. He gets the requirements, gives a quote and a date and goes from there. He is not greedy, so he is not trying to expand, more like maintain a steady rhythm of contracts.
He is not getting rich, but keeps himself busy and does what he likes...which honestly I don't know what it is, but it's not working.
