Here's a great one for the pre-school crowd. That age when you want to introduce them to paddling but they can't take more than about 20 minutes of sitting in a boat, and there must be a purpose to it. Like getting penny candy! Yes, actually 1 cent candy at the wonderful Judy's General Store on Mere Point in Brunswick. Judy's is part of Paul's Marina, which is a quick 20 minute (1/2 mile) paddle from the Mere Point boat launch. Judy's also has sandwiches, lobster rolls, baked goods, and ice cream. It's a good idea to call ahead if it's a busy weekend day and you want to order a sandwich. 729-3067
The Mere Point boat launch is great. It's big, with plenty of parking and a nice wide launch area and a couple outhouses. It can also be quite busy with boaters coming and going. I recommend trying this outing on a high tide, no-wind week day. Also, it's best if kayaks launch from the rocky shore area to the left of the concrete boat ramp to stay out of the way of boat trailers.
Once you're on the water it's a quick paddle north along the shoreline. Paul's Marina has a big T-shaped dock out front, and you can pull your kayak right up to the dock near the ramp. You should be fine to tie up there, but check in with an employee to be sure. Judy's is at the top of the ramp.
I did this trip with my daughter when she was 3. She sat in front of me in a large-cockpit kayak (possibly a 14' Pungo). The effort-to-time ratio is way off on trips like these, but it's well worth it to build a kid's confidence and comfort on the water a little at a time.