Sets of Three
The image above shows three groups of three objects. What we are trying to get across to our children in the learning numbers stage is that those groups are the same even though the contents are different and the patterns they make are different.
If you are using flash cards make sure that there is enough variety to get the point across. You can teach numbers to children using playing cards but often they are picking up on the pattern of the layout rather then the concept. For example they might be able to easily identify a three of diamonds or hearts but get confused if you drop three marbles in front of them and they roll apart, not forming a nice line like they do on the cards. Also if objects overlap it may be confusing too, if you put down three leaves and two of them over lap your child my think of them as one really big leaf and one small leaf.
There are really only two ways to get information to be retained by your brain.
1. Repeat it often enough so that the brain throws up its hands and says,"Okay, you've looked at this 25 times in the last two days it must be important, so I'll remember it."
2. Make it interesting, so your brain says, "Wow, that's interesting. It must be important I better remember this for later."
It also helps if you can link new material with stuff you've already learned and have found interesting. That is where most schools fall down. Math is almost always taught in a vacuum. It is never related to anything outside of math, except the occasional anecdote. It isn't like that If you clicked through the last post about Gauss his work in tracking an asteroid was important later to Einstein.