I've got a couple big ex-pro wrestlers contracted to come over at night and start breaking bones if I don't meet that minimum. It's a great incentive - you should try it sometime. I bet you thought I was going to name my kids as the biggest obstacle. They may keep me from writing during those peek, lucid daylight hours, but they have never been obstacles. Bedtime is a special blessing to every parent, once the kicking and screaming stops and the Nyquil kicks in, and the few hours that follow are your best chance at getting the work done.
Kids make great inspirations.
I've written stories about my kids, I've written stories about their toys, I've written more than a few stories about those specialized fears attached to having children that only a parent fully knows. That is why I'll never call them an obstacle. They are responsible for some of my best work. I've never been a writing mother, so anything I say is purely speculative. I imagine it depends wholly on the household.