Congratulations to both of you, I listened to all three movements and it is noticeable in the finale
that your son seems to melt a little; he certainly felt the tension in a particular way,
which is perhaps why he seemed a bit rigid to me, especially in the parts
played slowly, and it is precisely there that the touch is most clearly perceptible,
but this is normal; I think emotion also contributed to making
some parts be played slightly faster than the tempo you were keeping
with the piano, but this too is logically linked to emotion; I am sure
that by practicing at home (as often happens for those who feel these performances particularly strongly when an audience is present) you will have had a
different impression.
Regarding the cello's intonation, I would like to ask if, watching the video, it seemed to you
that the bow was positioned not quite at a right angle relative to
your son's body, because even here, it seemed to me that when
(even if the front view does not help) the notes were articulated more decisively,
the bow was positioned in a more effective way.
A compositional level, I liked the piece; if you think that the sonata form (even if
here on a smaller scale) is a form that I would like to know how to develop, I listened
to it with interest, and even though I do not yet have the means to analyze it (beyond
the score), it seems to me to be a well-developed work, and as others say, adequate
to an execution that is not particularly complex on the cello, but one can still notice
a good compositional ability and, above all, the ability to develop a theme in a pleasant way.