A good way to know how much Spanish you child knows is by quizzing them after their class and see if they actually learned something.
Practicing Spanish at home can be very effective and helps your child get in the habit of speaking Spanish. Try having a word of the day visible and easy to remember. Post it on the fridge in order to make it more accessible as well as more fun for the whole family.
As many of us know we learn a lot from kids, if you think your kid knows more Spanish than you do, have them help you. That way they will gain more confidence and it will encourage them to learn more.