I've never seen Laguna mention Squall being his son in the game and I've played through it 3 times, Laguna is never mentioned as a father either, I now he marry's Raine and she dies after heving a baby which was mentioned in the game only once, Squall is just one of those antagonist characters who have a mysterious past that family is never mentioned (wish I had that) so Laguna cannot be Squalls father.