Good post teamofthecentury.
I have two boys and I plan to let them play football when they're old enough.
From all the research I've been through, it seems that limiting impact until a child is 12 is very helpful. A child's brain is much smaller than his skull when they're younger, to allow growth. The precursor, or foundation if you will, of CTE has been linked to multiple impacts that cause the brain to slosh back and forth inside the skull. They aren't getting concussions, but they are jostling the brain quite a bit. When they do get concussions, it builds upon all that previous movement. So, having your younger children play flag football, then putting them in tackle when they're older will probably help. Plus, when a kid is older, he'll take coaching and training in proper form tackling a bit better, theoretically.
Soccer is tough on the skull because of headers. Anyone that played soccer knows, that ball is hard. You're taking it right on the head, and it sloshes the brain around the same way. The thing is, no one realized this. Coaches have their kids practice headers in practice, over and over. So, you're getting the reps that you would in football.