I have mixed feelings about these stories. Why should the grandchild have to suffer because his parents are irresponsible? I don’t blame the grandfather one little bit for feeling the way he does but if I had a great deal of money, which I certainly do not, my inclination would be to exclude the son (or daughter) from the trust, and pass his(her) share directly to the grandchild. That might actually have more deterince for this kind of callous, immoral, and irresponsible behavior. DNA testing would prove whether or not the grandchild was his.
“Why should the grandchild have to suffer because his parents are irresponsible?”
Because the trust document (apparently) provided for this specific circumstance.