takethatlady has pretty much covered it...
Personally, I can see potential benefits to children from both a SAHM and WOHM situation: I have no axe to grind relating to the positives/negatives of either choice because it's not a choice for me, I have to go back to work part-time or we would be financially crippled (and have to pay back a very handsome enhanced maternity package).
However, aside from the 'who is wrong?'/'who is right?' debate about women's work in and/or out of the home, I do wonder if constant adult-child stimulation and attention has the potential to create children who learn too late that the world doesn't revolve around them.
Whether a child is at home with his or her mum, or in childcare of some sort, I think it's healthy for them to be bored and sometimes benignly neglected. Children need to find their own solutions to the problems they face and not simply ours: at the moment, my 8 month old son has a habit of sitting on the floor and grunting at me in frustration that he can't crawl yet. If I make eye contact, he starts crying: he can't understand why I won't do it for him, for of course, at his age, he is the centre of the world as far as he knows. If I am "busy" but watching out of the corner of my eye, I can see him try out different movements.
This extends throughout childhood. As a speech and language therapist, I've come across a number of children with no particular developmental difficulty who have been late to talk as their parents have anticipated their every need.
The concept of a SAHM has been translated by the media (and many parents I know) into: I sit with my child and do crafts/play games/talk to them about everything/fill my day with relevant developmental "experiences"/respond to their every motion and sound e.g. a helicopter parent vs the WOHM who works full-time and struggles to find five minutes quality time with their child at the end of the day. I don't suppose it's like this for most women in reality but the stereotype seems to serve to provoke guilt in most women: what SAHM has the energy and time for that? what WOHM doesn't imagine a SAHM involves long days of sunshine feeding the ducks and baking (whether or not they would want to do these things, tapping into another level of guilt about "maternal instinct" relating to being your child's playmate).
As others have said, men are in the sidelines in this picture: they go to work, that and nothing more. Women make the childcare choices. We can choose to tut at the inequity of this and lament the failure of feminism, yet we do it to ourselves, we do, and that's why it really hurts. Women telling women that their choices are wrong, over and over and over... and buying into the guilt trap about WOHMs and SAHMs as though being one or the other (or a mixture of both) was a monolithic, defined entity.