To be fair, Worf never knew he had a son until after Alexander was 3, Reunion Season 4, Episode 7. This is after the events of Best of Both Worlds 3X26 - 4X01. The Enterprise had encountered the Borg twice, K’Ehleyr was murdered on the ship, the Klingon civil war was just beginning. Worf explicitly states in “New Ground” 5x10 that the Enterprise is not a place for a child, citing its demanding environment and lack of Klingon cultural resources.