Well I managed to keep my career going despite having 4 children under 5 years old at one point - I don't know how I did it as we have no family around to help and we weren't earning enough for a full time nanny. Somehow, we just did it.
When they were very little I took much time off in the form of maternity leave, unpaid leave and then when I had my fourth I went down to 3 days a week for the first 2 years.
Many many times throughout the years I felt like giving up, I was offered redundancy 3 times and was so tempted to take it as life was quite complicated and stressful at times.
However, now that my youngest is nearly 4, I am extremely glad I held on. Life with older children seems more expensive, especially for additional extras like music lessons, sports, kit, and days out/holidays.
I never saw it and never see it as a "forever thing" I always gave myself targets - the biggest target was to pay off the mortgage, now we just managed it the next one is to have some money saved, including for kids' university/or a small deposit for a house.
Once that is achieved I will probably consider taking redundancy, but we'll see how I feel when we get there. I definitely feel less desperate to leave work now than I did when they were little and it is true that things change as the years go by. However it is a very individual choice as I have a number of friends that worked full time when the children were little and now that they are all older and at school have preferred to stay at home for various reasons. Hope this helps a bit!