This is an interesting observation I have never considered before. There are hugh differences I my mind between the two.
If my son came in spitting sunflower seeds into a cup, I may think it is a little un-cultured and suggest to him he buy jars of already shelled seeds. If either one came in spitting tobacco juice, I would lose control quickly.
Another big difference is this. If your son develops a seed habit, they can stop it fairly easily, won't likely cause cancer (not that I know of today), and will cost him much less money during the habit.
That said, I understand the concern you have and say to you, if you don't feel comfortable doing anything around your son, don't do it period (except for the obvious with wifey). Personally, I used hard pretzels and canned nuts (peanuts, pastacios, peacans, cashews) so as to avoid too much sugar or aspartame from sugarless. Now, nearly 4 weeks into my quit, I'm starting to just not want pretzels, et. al. nearly as much.
Most important thing is to do whatever it takes today to not be a nic user. Other issues we can work on later when we're farther along in our quits.
Good job on surviving your first weekend of your quit. 'party2'