Hi,
I am a school psychologist, although I'm not currently working in a school (I have in the past). At this time I am employed part time (26 hours/week) by a private, non-profit agency doing developmental evaluations with children ages birth to 5, and I love my job!!

This is the age group I was hoping to work with when I pursued my PhD in school psychology at Penn State (I had an early childhood concentration), so things couldn't be much better. It's great knowing that you're helping to start kids off on perhaps a more successful path early.
As a school psychologist in the school system, my primary responsibility was to explore why children were having difficulty learning or frankly functioning in school and then to suggest strategies to help them succeed. It's a lot of testing and meetings, but there's also counseling, consulting with teachers and parents, etc... School psychologists are in a good position to assist with program evaluation, inservice training, behavioral support planning, and many other school related activities.
In terms of family-friendly, school psychology is a very family-friendly field. Typically, school psychologists who are employed by a school district work on a school calendar, which means having the same school vacations and snow days as your kids (including summers off!), and you often will end your day earlier than in 9-5 jobs. Currently, I'm on virtually the same schedule as my daughter, although I do work a couple weeks in the summer.
One suggestion: I would recommend spending some time in schools before deciding. A BS in psychology is a great accomplishment, but it helps to have some hands-on knowledge of schools, school systems, and kids/teachers in that environment. Perhaps you could volunteer in a classroom or trail the school psychologist (just a thought).
Best of luck with your decision!
Leslie