Can anyone cite any regulation that would prevent my child (not infant) from logging time for a private pilots license (i.e. 12 years from now when they are 16 for a solo, 13 years for a license when they are 17)? Background: I have children that I would like to start instructing and having them log flight training when they fly with me. I am VFR/IFR and medically current, and have a current FAA flight instructors license, therefore my question doesn't involve my own qualifications. Just if there are any known restrictions against the kid logging flight time. To clarify I don't mean both kids logging time on the same flight, just one kid. I have found none in the CFRs (e.g. 61).
If your child is going to be around airplanes and flying with you for the next 12 years, they're not going to need to log time from back when they are 4 years old. They will have plenty of logged time later in life.
I would suggest that you pick an age, say at least 8 or 10, where your children can start to fill in log books of their own. If they keep an interest in aviation until that time, getting their own log book that they can fill in themselves will be a big step for them to look forward to.