I use to work in a photography studio in Indiana, before I moved down here, so I can give you some pointers and/ or ideas. First and foremost, (which I'm sure you know because of being a wedding photographer) word of mouth. Tell anyone you know that you are getting into the family/ senior photography market. Second, you have a website, use it to advertise this. Also, use the clients you've had in the past with weddings, they are going to start families eventually, there's you family sessions. They have dealt with you in the past, and will more than likely be comfortable working with you again.
Advertise anywhere where there are kids. Talk to the owners of local businesses and see if you can place your photos on the walls as art (doctors offices, dentist, dermotogloy, local prom dress stores). You can also leave you information there when people ask about the photography.
You can always advertise in malls, but that can be very expensive. One alternative would be to advertise in the high school's newspaper and/ or year book. You could run "specials" for seniors in the newspapers. They are generally fairly cheap.
One heads up in the "senior" world. They want their senior pictures to be different, so if you can come with something different than you competition, then that will be huge for you. Also, you'll have to be digital. And you'll have to be able to use different digital looks (the grunge look, saturation, composites, etc.)
With baby sessions. Here's one thing the studio would do, and always had a great turn out; they would have special sessions throughout the year. Examples: during the summer we would have a fishing special, we'd have real water with plants and a dock, etc. For the spring (easter) we'd bring in real bunnies, a lamb, chicks, something diferent each year. For christmas, a big table, there the kids would literally make cookies, we'd have flour, cookie dough, cookie cutters, the whole thing, another year we had a live christmas tree with other misc. items in the photo.
I hope some of this helps. If you'd like to chat or had some other questions, feel free to contact me.