Hey, Welcome!
Any Antaresia are considered 'beginner' snakes, so that includes Children, Stimson and Spotted pythons. They're favoured because of their more docile nature, their relatively small size and their less complex husbandry needs.
However this is only relative to other snakes, I would say in general reptile keeping can be difficult and quite complex, there are lots of factors that go into meeting their basic needs and often it's not very intuitive as reptiles are difficult to read in comparison to a dog or a cat. As a result, responsibly keeping a snake often involves a tonne of continuous reading and research, especially at the start. Additionally even 'docile' species can be defensive/aggressive, theres no guarantee that if you get an Antaresia it won't bite your daughter, under the right circumstances all snakes bite and sometimes you'll just get a snake with a particularly feisty personality who will need to work with a lot more in order to be able to handle it easily.
This isn't to scare you off getting a snake, rather just to give you a heads up about some of the considerations that are useful to think about before making a commitment and choosing what type of reptile you'd like, snakes live 20yrs+ and because of their sometimes complicated nature, your daughter will likely need your help quite a bit, at least in the first year or so. If you're cool with this, then I think Antaresias are a great place to start!
What type of enclosure do you have and what are its dimensions? this could also greatly impact what type of snake would be suitable. Additionally, If you are planning on getting a snake from when its a hatchling, you usually start with very small plastic enclosures/tubs and then work your way up to the full sized enclosure.
As far as where to buy, some specialised brick and mortar pet stores carry snakes but you're more likely going to find them online. Either through online pet stores or websites like this, here you can find snakes for sale under the Marketplace tab, or websites like the reptile classifieds where you're usually buying from breeders or previous owners. Before you buy, make sure you look into the licensing requirements for your state, if you don't do this properly your snake will be considered to be illegally owned which is a whole can of worms you don't want to have to worry about
Good luck!