Was Yishmael's mocking malicious, or just childish play?
Sforno
Sforno attributes Yishmael’s mocking to the negative influence of his mother Hagar, the Egyptian, reasoning that since Avraham never spoke disparagingly, the boy must have absorbed such talk from Hagar; his taunt specifically repeated gossip suggesting Yitzchak was really Avimelech’s son, gossip he only later overheard. Ibn Ezra, by contrast, sees nothing sinister in Yishmael's behavior, viewing it as ordinary childish playfulness, and attributes Sarah's reaction instead to her jealousy over Yishmael being the elder son. Thus the two differ on whether Yishmael's "playing" reflected malicious intent rooted in his upbringing, or simply normal child's play misread through Sarah's jealousy.AI summary · anthropic/claude-haiku-5.5
“Sarah saw the son whom Hagar the Egyptian had borne to Abraham playing.”
את בן הגר המצרית — she assumed that the reason Ishmael had made disparaging remarks about Yitzchok was due to his mother putting him up to it, or to the Egyptian genes of his mother coming into play here. We have a saying in Sukkah 56 that the prattle of children in public reflects either what they picked up from their father or what they picked up from their mother. In the case of Ishmael, he certainly did not overhear his father make such disparaging remarks.
מצחק — making fun of the big party Avraham had given to mark the weaning of Yitzchok, He claimed that surely Sarah must have become pregnant from Avimelech. The reason he had not made such remarks already at the time when Yitzchok had been born, was because he had only overheard wicked gossip about this at a later stage, and now he repeated what he had heard.
Ibn Ezra, who reads it differently
MAKING SPORT. — Ishmael was acting as a boy is wont to act. Sarah was jealous because he was older than her son.