Children usually start to learn about decimals in Year 4. The first thing children need to know is that a decimal is A PART of a whole. A good way to explain this is to show them an empty hundred number square / chart.
Ask family to quiz you on your multiplication tables. Once you have studied them enough to know them well, ask your family to quiz you on the tables you have just learned. This will help you remember them long term and keep the numbers fresh in your head. When you have all the tables memorized, ask them to quiz you on all of the numbers, not just one number at a time.