I can really relate to the feelings you are talking about - especially when you have such very young children/babies as they are so reliant on you. Things do change so very rapidly as everyone grows up.
I have struggled with this and ultimately decided that I should stay working. This was a result of having to make a drastic change in our living standards if I chose to opt out. One one hand if I gave up my position I would not get it back - one the otherhand luckily my employer has to let me work part time so I haven't had to decide about full time care.
My experience was that going back after DD2 was much easier a transition than previously as well, partly because I knew what to expect and also was more organised about our routine and had more realistic expectations of myself and what I could acheive. I was also greatful for the adult company and mental stimulation as well by the time my mat leave was up.
I am now almost 3 years away from that choice but I have been recently surprised by seeing how many of my friends/contemporaries are now looking for work - particularly the mums of DD1's prep buddies. Many of them are struggling to get interviews in their chosen fields at a reasonable level let alone get jobs. This has made me grateful that I kept at it (despite feeling like I was struggling or at times even failing with all tasks at hand) and I am surprised by how this situation has affected many others.
My other point is quite blunt - both DH and I have experiences of parents either passing away unexpectedly or never working again after illness. Me working takes the pressure off DH and quite simply means that should the need arise I have the ability to provide for my kids. I already feel the pressures on my sick leave etc that having kids has had but at least I have those entitlements to call on.
Good luck with your decision making - try to plan for 2, 5, 7 years down the track and see how you can try to acheive all you want to. If you can buy more time to consider your options I would tend towards that as well. You may be surprised where you end up!!! xxx