It appears that the children of two dwellers are some combination of the statistics of their parents. But do the outfits they are wearing at the time factored into their stats?
I have had many births in my vault, and when i put Old Longfellow, 5 Strength 7 perception 8 endurance 4 charisma 6 intelligence 3 agility and 7 luck with my highest girls example: agility 5 with 2 or 1 everything else. i gave them outfits and bred and they got about a 4-6 everything. When i bred them without outfits that have +3-4 in stats, it changed it to a 3-6 stats three times in a row. Not a big difference, but it still works.