I hadn't seen you'd posted your hours fourtothedozen so apologies for that. If you only work 10 hours a week, unless you're sure you'd only be working 10 hours a week if you didn't have kids then yes, it's costing you income. Not necessarily the figure you give, as it's possible you wouldn't be able to and/or want to get full time in your field, of course. But even if we assume you'd have stayed in the less lucrative job, 18k is less than 24k.
And to answer OP's question:
Hypothetically speaking, if you or your partner earned enough to keep you going (e.i. enough to live but you wouldn't have all the luxuries), would the other stay at home?
No, I wouldn't and neither would DH. We could both cover enough to live and some luxuries on a full time wage, his being more than mine because I've spent the past couple of years having children, working part time and being on (not especially long) MLs. For a lot of reasons:
- We know our small children will get more expensive as they get older and want to be financially prepared for that. For us, staying in work is the best way.
- Insurance. I have experience of being brought up in a 1 WP, 1 SAHP household in the sort of situation you describe, and things then going tits up. I don't want to repeat that. It made me perhaps more risk averse than many, and so DH and I have prioritised tailoring our lifestyle to be affordable on one income if necessary. Of course we're lucky to have this option.
- Pensions. I don't expect the state one to be worth very much or available until I'm 193. And ability to save. Only one of us being in work in the situation you describe would mean no financial cushion if the shit hit the fan. I didn't much enjoy living on benefits even as a child, I doubt it'd be more fun now. Both staying in work reduces the risk of this possibility.
- Both of us are in lines of work where you need to keep your hand in. A couple of years out would screw both of us, for different reasons.
However, I freely admit part of the reason this is such a no brainer is because we're in a fortunate position wrt part time work, flexible work, free preschool place kicking in soon and extended family members who work in childcare.