Mothers generally know this trick. It works especially well with food children do not want to eat, but must.
Tell the child that he only has to eat 3 bites. Then let the child eat just that many bites, which you can count together if you like. Increase the number of bites as the child learns to count. Alter the exercise with how many peas can be left on the plate; how many bites can be exchanged for another food or desert, and other tricks.
As the child learns fractions, work with eating (or leaving on the plate) 1/2 of the food, or 3/4, or other familiar fractions. Fill glasses 1/2 full of their favorite beverage and offer another 1/3 or 3/4 or so more when he drinks the first fractional amount.
Conversations and expectations and games like this applied to food and drink, picking up toys, helping out around the house, etc., help children from ages 5-7 develop their number sense. These tricks can be used just about every day for a few minutes a day--longer only if the child likes the counting activity.
If the child starts to bargain with numbers and fractions, let him/her. Bargaining initiated by the child shows that numbers are becoming real to him/her. A few weeks of such bargain, or a limit of only one bargain per meal for a few months will allow the child to eat enough and still learn numbers. Bargaining this way gives the child confidence and a sense of control over his world. You still maintain control by limiting the number of bargains that can be made per meal or per day, and by limiting which issues are subject to bargaining and which are not. Again, observe your child for positive signs of accomplishment and confidence. If these are improving or growing, consider allowing the child to bargain over something you might ordinarily have said no to.
What tricks do you use with your K-2 child? Is your child ready for these tricks as a pre-K activity? That depends on the individual child. Children must grow into a readiness for learning math skills. This growth occurs at a different age for each child. Generally, children are ready to learn to count during pre-K, and ready to think in terms of 1/2 (although it may be called 2 [equal] parts) when he/she learns to share a cookie or large piece of candy. Thinking in terms of 1/2 is common to most kids by the middle of the 2nd grade, and used by many children months before then.
Don't be concerned if learning takes time--even months. Readiness to learn means that the child can begin to learn, not that the learning is easy or automatic. And Readiness happens when it happens. Learning can take place once the child is ready, but before that time, expect little retention of a lesson that is beyond the child's readiness. Readiness is kind of mental growth and growth can't be forced. It can be gently shaped and fostered, but not forced. If your child is not learning, give it time and keep up the fostering of learning activities. Unless the child is many months behind the learning of his classmates or same-age friends, there is no need to be concerned. If you do get concerned, by all means talk to your child's teacher. Potential learning problems caught early can often be helped early, giving the child a greater potential to advance according to his/her abilities.