Statistics for disposable income by family size is hard to get (I don't think the US census measures that). My gut feeling is that dual income, no kids families are going to be at the very top because not only are kids incredibly expensive, but not having kids means that you can concentrate on work. Having said that, family size will also skew around age so it's really hard to say. I'll just say that I've never met a family with kids that isn't concerned about money.

But even having more money, will people buy robot appliances? Again, my gut feeling is that singles are actually more likely to buy things like that because the downside of making an ineffective purchase is dramatically lower.