How do you put thinking about them to one side (apart from the practicalities of juggling childcare)?
This almost seems funny to me, this statement.
You get the best childcare you can get, so in my case, dad staying at home for some time, granny and also paid childcare- and then you delegate it to them!
For that time, those adults are in charge, not you. It's incredibly liberating to realise that, in fact, your children are fine and manage fine without your constant supervision. That doesn't stop you being immediately attentive when they get home from school/you are suddenly needed.
Also, in fairness, I work (in a demanding job) in a family friendly place, where no-one is clockwatching, so if I need to leave early to do pick-ups or drop everything in a sudden emergency, then I do so- the men do too. So, I am not forced to suppress my role as a mother in this situation (though I rarely speak about children with colleagues, only good friends).
My very unscientific survey of my friends suggests that the women that cope best in terms of identity do indeed work full-time. I don't think this is only because they have a 'work identity' (actually for a lot of women, being seen as a mum in work isn't a great thing)- it's because, having got used to having children having childcare and not being dependent on just them as carers, they then tend to do more things away from children- such as the odd night out with friends, or go away with work. They seem to retain more of the old them, somehow. I have friends who are SAHM whose husbands have literally never had all three children on their own (and profess themselves incapable of doing so)- no wonder they feel their identity seeping away, they don't get any time off!
It also changes depending how little your children are, it's all consuming being a mum when they are tiny, even if you are working I found- but once they are a bit older, everyone is their own separate people and you come together to do fun stuff, eat meals, chat about issues, not just because you are tied together like when they are tiny. This then allows you to get back more of yourself, in terms of going out, doing stuff as a couple, reading, hobbies, whatever you like to do.
I don't think it matters so much whether you work or not, but about to what extent you get some time to yourself (I imagine if you had a child with very profound special needs this would also eat up all that 'spare' time and make being you separate to that very hard) and get to do things that are important to you beyond having children.