Okay, so basically there are two types of offspring: precocial and altricial. There are gradiations in between that are recognized too, especially in bird species, but we're not going to discuss them here.
Precocial young are relatively advanced when they are born, able to move on their own, can eat solid food, and already have some behavior patterns developed. Mallard ducks are an example. For instance, the mother, while incubating the eggs, emits vocalizations (which are similar to the ones she will use to call the babies into the nest later). So she thereby imprints her young to her voice before they hatch. Soon after hatching, the young are ready to leave the nest, but recognize the mother's voice and return to the nest when they hear it (Drickamer et al. 2002).
Altricial young are very helpless at birth, requiring lots of care and maintenance from the parent(s). They usually cannot move or eat on their own, and usually cannot even eat solid food. Songbirds and parrots fall into this category. Obviously, so do humans.
Now, evolutionarily, parents want to have as many offspring as possible to pass on their genes. However, each offspring requires an investment on the part of the parent (which will be different depending on the gender of the parent, their degree of involvement in incubation, nuturing, etc.) Parental investment includes any investment by the parent in an individual offspring that increases that offspring's chance of surviving (i.e. reproducing) at the cost of that parent's ability to invest in other offspring (Drickamer et al. 2002). Usually females have a higher reproductive cost. (But we women already knew this; it takes the men to reason it out and write it down to realize it I guess). Parents will invest more time in fewer individual young for several reasons: when their own chances of surviving decrease; when food is hard to obtain; when they are sure that the offspring is their own (and they want to make sure the genes get passed on. However, the parents should not invest too much care in just one offspring, unless that's the only chance they have. From the offspring/child's perspective, they want want lots and lots of care, because this will help their own survival and ability to reproduce later on.
What this means is that, from an evolutionary standpoint, children do not see activities such as washing dishes and talking on the phone as contributing to their overall survival, so they try to force you to pay attention them instead. This also shows up as sibling rilvalry. Of course, at some point, they should realize that it is safer for them in the long run to let Mommy finish doing the dishes before they harass her to play games, because otherwise they will end up helping.
