Question about being unpressurized at higher (Class A) altitudes

My father has a C182 in which I have been to about 10K ft MSL. I am
currently working on my license and am considering building a Velocity
or Aerocanard, both of which have ceilings up into Class A airspace,
one as high as FL250. (Before anyone cautions me about building one
of these, I know two people with Velocities and a local builder who
has built multiple canard aircraft. I will have lots of support and
will have logged PIC time in one long before mine is built.) While I
know that oxygen is required at altitude, what is the effect of the
lower pressure on pilot and passengers? I am doing this in part for
the purpose of transporting myself and family to visit friends and
relatives and am curious about the effect on my two children,
currently 3 and 5, and whether this will make them less pleasant to
fly with.

TIA