It didn't "hit" me before Incredibles 2, but why is everyone (or at least the Parr family and Edna Mode) surprised that Jack-Jack has powers?
While this answer doesn't really explain where Supers get their powers from, it concludes that two Supers should produce a Super, which is true for Violet and Dash (and then for Jack-Jack obviously).
Like I said, if I only ask the question now, it's because in Incredibles 2, Edna once said something like "It often happens that baby Supers have multi powers, but not that much", which accentuates the fact that baby Super have powers!
So, why is everyone so surprised that Jack-Jack has powers?