Set end of time limits. You can only play for 5 more minutes, then we have to go catch the bus. At first your children won't know what the minutes mean, but gradually the children will understand the idea of time passing. This uses counting to help children develop a sense of the passing of time. It is not until children are older that they understand more abstract notions like yesterday, today, and tomorrow.
Fractions represent parts of a whole.
A very young child will see something cut into three pieces and will believe that there is more after cutting it than before it was cut. This is typical and should not cause alarm in parents. Cutting up pizzas or sharing a pan of brownies are good ways to get children thinking about fractions. To estimate accurately, numbers and size have to have meaning. Very young children will not be able to estimate accurately, because they are still learning these concepts.