A good understanding of the base 10 number system is required in order to allow your child to successfully work with decimal numbers.
When teaching decimal numbers, first review the basics of thousands, hundreds, tens and ones and then introduce (or review) tenths, hundredths and thousandths.
Be careful when discussing tenths, hundredths, and thousandths with your children. Pronounce these terms with special emphasis on the “-ths” to help avoid their confusion with tens, hundreds, and thousands.
Start from the left. i.e. if the tenths are bigger then there is no need to compare the hundredths.
These tips, together with the resources on this site will help you when teaching decimals to your child.