It depends on a number of things. The relationship of the child to the deceased, the type of service, what did you tell the child about the passing of the person (that they went to sleep for a long time is inappropriate, kids will fear sleeping and not being able to wake up)... just for starters.
My Dad passed away when my kids were 9,7, and 4. All three went to the services. All three of them were a part of his living with his lung cancer and they all knew that he was going to die. Heaven was the only place where Poppa could go and get well. They experienced his trips to the hospital, the oxygen tanks, the nebulizer, his hospital bed in the living room that he took them for rides on, his continuing undying love and interaction with them. When I got the call he had passed away we were on a vacation in Disneyland. (We were due to fly home the next morning.) We had gotten back to our hotel room for the evening and the fireworks were just beginning to go off. I got the call and all three of our kids started jumping up and down on the beds, hollaring "Yeah!! Poppa's in Heaven!! He doesn't hurt anymore!! Yeah!!" Do they miss him, YES. At the service, there was no body, my Dad wanted direct cremation. It was a celebration, a rememberance service of his humor, his escapades, his hard works, his love for his family and friends. At the end I had balloons for the grandkids (I have two nephews, one who was 4 and one almost a yr at that time), they hugged their balloons, put kisses on them and let them go up to Poppa to catch their hugs and kisses. 3 yrs ago, my sister-in-law passed away unexpectedly leaving behind a 10yr old son and a 5 yr old daughter. Her children were able to be with her at the hospital before she passed, they knew that they were having a tug of war with the angels and the angels were going to win. Again, there was no body at the memorial. They had picked items to send with their Mom and my nephew sent his wrestling trophy and 2 of his 1st place medals. They were cremated with her. Again, her memorial was a celebration, a remembrance of her life. And for the kids, it's important to hear all those stories and tales. I had placed 4x6 recipe cards on the tables (huge potluck) and asked that folks write down their favorite stories, tales, jokes that their Mom had told them. These weren't to be condolensces, but memories, good times. Then I put them in 4x6 photo albums for the kids and mixed photographs of their Mom in with the cards. This is a place where they can go and find a piece of her, anytime. As far as your teenage son, those teen years are hard. Talk to him about his feelings about the person. Funerals aren't for those who passed as much as they are for those left behind. He might not need to go, but his going might help someone else deal with their grief, help them remember a good time. Talk. And then there is you. Do you need your kids to be there? Ask yourself why and you'll have the reasons you need. I wish you peace.