Well when you are a teacher with young children this will always be a problem so you need to sort out now how you are going to work it.
It is easier in some jobs than others to take time off eg work from home/take flexi/take holiday/unpaid leave. You can't do that in teaching.
Also when you are not there you can disrupt hundreds of people in one day eg a secondary school teacher might have five classes in a day plus a form class = 180 pupils to be covered plus maybe a break duty or meeting or assembly. So there is the guilt of letting down all those pupils (they might have exams) and the worry about the number of colleagues you have pissed off who have to set your work, possibly cover your class, do your duty etc.
At least there are the two of you plus a childminder and a nursery for childcare. I became a single parent when I was teaching and it was impossible to cover illness, appointments, inset days, sports days, Christmas concerts etc for more than one child.
Some headteachers are more sympathetic than others but these days they have LA policies to follow and I found they got stricter about time off and I had to give up in the end.
Do you have family to help in emergencies? Are you planning to have more children?
I would say it is fair to take it in turns but it depends on the knock-on effect it has on his work and earnings too. It is particularly important that you are there in your training period as obviously you are being assessed and you will need good references to get your first job.