This is a process. You begin now if you have not already. Most ten year old males are curious about body changes they or their friends talk about. However you are comfortable, start the conversation. Ask your pediatrician who may have literature or suggestions for you. Start simple and keep it open ended--let them ask you questions about what they see on TV etc.. use every opportunity that makes sense to provide support and good information.
Wayne Yankus, MD, FAAP
expert panelist: pediatrics
We started with the basics around this age, then added any details as question arose. We tried to make it more scientific when they were younger, but added the emotional connections as they aged. My kids are older, and still ask questions, most still make me uncomfortable, but they deserve an accurate answer. I would prefer they be able to ask us than get possibly wrong information from their friends.
My son is 12 and when he was 10 he started asking all kind of questions to his friends he plays with online so that told me that we needed to have a talk about the different changes boys go through and now days the kids are starting things way to soon if Im asked, but what to do but explain it to them the best we can or get advice from family doctor