I can see why you are anxious about this transition because it is a BIG change to YOUR lifestyle. Although it would also be a change for your children, I think they would choose you over any daycare environment. YOU are MOM! :)
I went from working full time to being a SAHM (who works very limited part time) with my first....not quite your situation. I also worked with children (and still do...I tutor privately).
My advice is to go for it! It sooooooo worth it. I get to cuddle my kids anytime I want to and they get to cuddle their mom anytime they want to. I answer the questions they ask with my values and our lifestyle in perspective, not someone else (even as great as they are).
Logistics:
* You already know how to work with kids and plan activities...great. Just don't over plan or over do things. Kids need some down time.
* Look into community education courses or Early Childhood/Family Education programs (Here we have ECFE classes....1.5 hours a week per child)
* Locate other SAHM's in the area and plan playdates and meet up at the park, go to museums, etc. with them. It may take a little while to find other mom's with similar parenting styles, but it is a GREAT way to make friends of your own while your kids play. You can look on this site, google your area for a mom's group, or create one yourself.
As far as making extra money....what can you do as a service for someone else? You mentioned you worked with kids....can you provide before or after school care for some local kids? Tutor? Provide short term babysitting for other moms who have some errands to run?
Are you able to pet sit? Do someone's laundry? Assist a homebound person with errands? Try www.care.com to find or advertise these types of services.
What a great opportunity for you! And yes, there are days when I wonder if I can do it, like today. I have two sick kids and am still in my PJ's. I'm squeezing in my computer time with my lunch while the sickest sleeps. I wouldn't want it any other way. I get to spend quality time with my kids.
Oh....and you'll want to schedule a night out with friends on a regular basis. That will help give you adult conversation and help you appreciate your kids all over again.
Good luck with your decision!
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