Hi,
I´ve had 3 snakes, now only one, a kings phyton is left. I did never have any problems with it regarding my health. But your daughter is quite young, so who´s gonna feed the snake? Does she know that a snake is fed with "cute" live mice, hamsters or something like that? And would she like to watch the mice beeing strangled? You do also have to be quite careful when feeding snakes, because when they smell their food, they are very fast and you have to keep your hands "out of the way". It may also last a while until the snake is used too be touched, so it might bite sometimes.
The next point would be what kind of snake? A cornsnake for example is very nice to look at but is moving very fast and quite thin. So when you want to take it out of the terrarium, you have to watch that it doesn´t escape and vanish. For the same reason the terrarium should always be securely locked, no matter what snake you have, because they will find every open space, no matter how small and use it!!! For a seven year old, that could be a problem too.
A frog is in my opinion no animal for neither a 3year no 7year old, because its much too sensitive. Its no animal to play with and to be touched too hard, unless you want to buy a new one every few days...
I got a turtle when I was 7 years old, but - as always - my mother did most of the work and its also more an animal for watching not for playing with it! If you go into a zoo and watch small children looking at reptiles, you will notice that they get bored very soon, because the animals don´t do much instead of sitting/laying around.
At that age I think dogs or cats are better for kids, because they can play with them and they have the possibility to go away, if the kids touch them too hard or something like that.
Uli,43,Germany, cf/cfrd