Judah wrote:
Roger wrote in
:

That is not an option. The parent can not take responsibility that
belongs to any of the flight crew. It is quite likely that some time
in the not too distant future even infants will have to be in an
approved seat restraint at take off and landing.

What documentation is a parent required to provide in order to fly a 2 year
old on his lap?
No amount of documentation will change this. You can't fly with a 2
year old in your lap. Under 2 you can but 2 or older must be in a seat
with the seat belt fastened