I started backpacking with my kids when they were infants (I carried them), and have spent a lot of time backpacking with small kids.  They are teens now, and both of them still backpack with me. 

 One thing my kids really hated when they were little was if I didn't know where we were going to stop.  During that stage it was really helpful to reserve backcountry campsites at a National Park so I could point to a map and say, look that's where we are going and I can't change my mind because it's reserved. 

A 10 year old might like to bring a stuffed animal or a favorite toy, even though that's extra weight.  My teenagers still like to bring a small stuffie (they have Folkmanis finger puppets). 

From the start I made my kids carry the things they might need during the day so they wouldn't have to ask me.  Their standard day pack has a sun hat, a sun shirt, a rain poncho, a water bottle, sunscreen,  lip balm and a tube of afterbite (not sure it does anything, but it made them happy when they got a bug bite). They each have a  small bag (Sea to Summit 1 liter lightweight dry sacks) to fill with their own selection of snacks in the morning before we hike.  Now that they are teens, they still fill water bottles and snack bags before we hike (and they still like to hog all of their favorite snack).

It will help drum up some excitement to let your son buy something for the trip, My kids were very excited about freeze dried astronaut ice cream, but even about things like rain ponchos, mess kits and water bottles if they got to pick their own.  They really like to have their own gear and not just "borrow" it from me. 

Make sure you aren't the one doing all the work.  Give your son tasks like setting up the tent, getting out the sleeping bags or fetching water.  If he's like my kids, you should let him try to do stuff himself and he'll ask you for help if he needs it.   My kids especially love getting water, particularly if it's a spring you can drink from but even if you have to treat or boil it. 

When you get off the trail, stop for ice cream on the way home and make it a tradition.  That way you can talk about how good the ice cream is going to be during the trip.