What I do, if I took three years out (or more, many have multiple children), the industry and the work would have changed so dramatically that I couldn't just go back. I took just over a year out for mat leave, because of how the AL accrual worked for me, and had to work twice as hard to figure out all the new ways of working, the new technology and the changes to the company. Triple that and I'd have to go back to entry level, if I could get in at all.
And my employer needs someone doing what I do, so if I'm not going back after mat leave they have to backfill my position. So my role isn't there to go back to. Where do I go? Do I start building my reputation again? From the bottom? Or do I take the flexibility and good will my previous hard work and reliability has afforded me and use it to my advantage to do my job and still be around for my DD whenever necessary? As well as giving her socialisation and activity that she really enjoys.
Aside from that, who's paying for my pension? Who is making sure my shares and investments are still being put into? Who's planning for my retirement once my child is grown? Because all of DHs earnings are going towards keeping us afloat day to day. There wouldn't be anything left after that to plan for our retirement. And three or four years can make a massive difference to those things.
If I take multiple years off work and DH leaves, or dies, or is suddenly unable to work, is that entry level position I have to take going to keep us afloat? Is it going to pay all the bills AND let DD have the activities she loves (swimming, dancing, gymnastics, anything)?
Have you thought through anything other than your own belief that mothers should be martyr's to their family while fathers get to continue progressing their careers and earning potential?