In my opinion, I think that you should focus on providing more indepth learning experiences for him rather than advancing grade levels. As homeschoolers, you have the flexibility to teach him at his level, wherever it is. If he really wants to graduate early and go to college early, then you can, of course, have him take the SAT or ACT and talk to the colleges about him enrolling at a younger-than-typical age. But if it were my child, and I wanted him to be a child (as you stated above), I would use this time to provide all the fun and indepth learning experiences as possible while he's still at home.
Learning is a journey, not a race, and college is a totally different social scene. Over my 20+ years of homeschooling, all of the parents and students I've known personally (public, private, and homeschool) who've graduated and entered college early have regretted it. I'm sure there are others who didn't/don't regret it, but I don't know them personally.
You don't have to prove to anyone (nosy neighbors or school officials or other parents or whomever....) how smart your son is, so the pressure is off. I wouldn't even worry about credits until high school. If he takes Algebra 2 or Calculus or Spanish 3 in the 9th grade, and higher level maths and Spanish each year after that, list those courses on his transcript. College admission officials will know he had Algebra 1, Spanish 1 and 2, etc., before that. You don't have to list tons of credits on a transcript to prove your son is smart - his SAT/ACT scores, foreign language college placement exams, and interviews will establish that, without making it seem that your son was so focused on academics that there was nothing else in his life. (If that makes sense.)
If he decides to enter college at a younger grade, then it would be best to talk to any colleges he's interested in to see what their requirements are for younger students, etc. Then you'd have to list courses/credits, etc., on his transcript to show that he's met their requirements. But if he decides to enter college with his age-mates, then the pressure is off, and he's free to learn at will. You can worry about paperwork and documenting coursework when he enters 9th grade.
I hope this helps. Let me know if you have any other questions.