That is mostly because infants constantly put things in their mouths. If the child doesn't handle the reptiles they should be just fine. If you do let them touch them then wash their hands afterwards. It's all mostly just common sense.

In a lot of localities it is illegal to sell turtles with a shell length under 4 inches. This was enacted because toddlers would put them in their mouths and some would get salmonella that way. I have 23 snakes and have kept various types of reptiles for years including the previous nine years (the age of my oldest). I have 3 kids and none have come down with salmonella. If you use sound husbandry practices (ie. keep things clean and don't let them put their hands in their mouths after touching reptiles) then your family should be fine.