If you would like to purchase a calculator for your child to use at home, the models I would consider are the TI-84 Plus or the TI-84 Plus CE. They are on the expensive side, but they will be used all through high school and can be used on tests, so they are a good investment.
If you would like a free calculator they can use on their phone, you can download one from below. Remember that these calculators can't be used on tests or in class. They'll still be expected to use the TI-84 Plus calculators we provide in class so that they are comfortable using them on tests and other assignments, but these are a good tool to use for homework help.
I will teach you most of what you need to know about our calculators in class, but in case you forget, here are some links to help: