Ahhh, the decision between career and family. That's something I'm struggling with as well right now, though for different reasons.
I think you need to look 5-6 years out and ask yourself "what do you want to be doing?" Once your youngest child is in school, will you want to be in the workforce? If so, you should go ahead and continue forward with your plans. You aren't pregnant with the second one yet, and it could take a while - or happen right away.
We didn't purposefully wait 14 years between children, our youngest just happened - what a blessing - but he happened just after I'd been on a new job for a little over a year. I understand the guilt that comes with taking maternity leave so soon after starting a new job. If you're going to continue teaching after the second one comes along, go for it! Don't worry about "what if", you can't know for sure when you might get pregnant. Really, you can't know if you won't be in an accident or that a family member will need your assistance, either, and both could result in you taking long periods of time off of work in the first year.
Make the choice that's right for you not only now but in the future and all will be well.