(Almost pastor) David asked (here) about the numbers in our Bible School vs Sunday School. I thought I'd answer in a post rather than in a comment.
The Bible School combines the energies of two churches, our Lutheran Church and a small Covenant Church. I don't know how many of the children were from the Covenant Church and how many from the community at large, including summer people and grandchildren, etc. It has been common in this town for people to send their children to the various Vacation Bible Schools at the other churches. For the last several years, only the Baptists and the Lutheran/Covenant churches had a Bible School.
It is also not uncommon for people to send their children to a Bible School for some free day care. We are careful to not accept kids under the age of three unless the parent wants to be with that child full time.
Our town has about 615 residents, most of whom are senior citizens. But there are many people in the surrounding area, including summer residents.
Attendance at church is about 150 - 180/Sunday year round, with a somewhat different group attending in summer because so many of our residents have employment that keeps them busy on Sundays in summer. We have several retired pastors who attend in summer.
All the school districts around this area have had their census drop dramatically to the point where some schools may have to combine and/or close.
All these points are leading me to answer David's question. Yes, our Sunday School is very small compared to the VBS. And it is really small compared to about 15 - 20 years ago. This is partially demographics, as pointed out above.
There are two other factors, I think. More women work. I think that this leads to Sunday being the one day when the mom can sleep late or get to the store in a leisurely manner. There have always been kids dropped off at Sunday School, whose parents don't even come in the door, but now even this seems less regular. We've not been successful in getting the young mothers to help with Sunday School. The young mothers like to have a bit of a social time while the kids are at Sunday School. [It might be a good place to start a mother's group.] Most of the teens work too, usually on weekends, so we aren't doing a good job at getting teens involved with teaching the children like we used to.
Our pastor said that one of the mother's complained that her child wasn't getting much of a Bible education, yet she brought the child only intermittently.
Another possible cause of the Sunday School problems is the curriculum. We used to have a traditional curriculum. That coincided with the larger attendance. The leaders changed to a type of program, called rotation Sunday School, in which the stories are told in various ways over the course of a few Sundays. The kids have been dropping out. Maybe the parents don't think there is any 'meat' in the lessons.
Times have certainly changed. The active people in our church who are in their 50's were the active people when they were in their 20's and 30's. The current pastor is a bit more "user friendly" for young families, and we have a fairly new youth director who has some responsibility for Christian education, with the main work still being done by volunteers.
I was the Sunday School Superintendent during the mid 90's when the program was large and traditional. Because of changing demographics, I think the program would have shrunk no matter what. My bias is that the change to the rotation Sunday School accelerated the drop in attendance. In addition, we had a year or so during which a number of young families left for another church which has an extremely active children's program.