And where exactly does it state that 79.7 million only includes the adults? In any case the numbers still do not add up to 66 million Christians. Show me the numbers, not the hand-waving. (The enabling act was passed by the Reichstag and not the general populace, so your statement is rather meaningless since a cooperative effort can start with any number. Further all those banned parties count somewhere, and if they are not a substantial amount why are they a danger?)
Given that:
66% L - Lutherans & other Protestants
33% C - Catholic
1% J - Jews & others.
Solve for C such that:
L + C + J = Ptot = 79.7 million.
and
0.66L + 0.33C + 0.01J >= 0.89Ptot (margin approving the 1934 Fuhrer referendum)
and
0.66L + 0.33C >= 0.98Ptot (margin in favor of the 1938 Austria anschluss)