I don’t post my kids pictures on Facebook either, but it has more to do with privacy than anything. Right now I have 402 “friends” on Facebook. Some of those friends include real-life friends and family. But a lot more of those are business acquaintances or fellow writers. A lot of them are people I added because it’s easier to add them as a friend then exchange phone numbers.
Not everyone who is my “friend” on Facebook needs to know what my children are doing or interested in. Some of them don’t even know I have children — and I’m okay with that. They don’t NEED to know. They need to earn my trust first. In real life.