This post is at the request of Nikkilina. I welcome any and all suggestions for topics.

Infants are such simple little creatures. Their heads are too big for their bodies and they often smell. However, they do grow up and later become productive members of society, like bloggers or webcomics. However, while small and under-developed that are capable of doing some amazing things. Amazing being used in the sense that 'they amaze us', not in the sense that they are capable of impressing us.

Infants and toddlers all lack a Theory of Mind. All adults have ToM (though it might be argued some more than others). ToM is the capacity to infer states-of-mind of another, this encompasses beliefs, desires, intentions, pretence, attention, and knowledge. It is both the capacity to understand one's own mind in relation to others, and understand the mind of others in relation to the self (and others). It exists on a continuum where new-borns have an incredibly limited capacity for ToM and it develops, gradation by gradation, module by module, until, as adults, we can function in this highly cohesive, deceptive, co-operative, threatening, and engaging society.

To give quick preface on its development for those who are not familiar with it. Newborns develop the ability to detect whether someone is looking at them between birth and 16 weeks. Between 3 and 4 months after birth infants are capable of following the gaze of another; 4 to 5 months after birth they develop the capacity to detect animacy, that is, they can tell that people and pets and things move on their own, but a leaf blowing in the wind is not really animate. It's not perfect however, they're likely to infer that a remote controlled car is animate too. Between 5 - 8 months they can detect a goal in another, that is, they can open doors for people who's hands are full, or pick up dropped objects, or help someone reaching for an object that is out of range. The ability to understand joint attention emerges between 18 and 24 months (i.e. understanding and correctly executing pointing); pretend play (the ability to differentiate personal reality and fantasy) emerges at this time also.

Now for the big stuff: Between 2 and 3 years they learn to infer desires and intention; between 3 -4 they gain meta-representation (the capacity to think about thinking, or understand concepts as something other than themselves); between 6 - 7 kids learn to distinguish between lies and jokes, and from 9 - 11 they understand faux pas (a deceptively subtle example of ToM, but actually a very sophisticated process).

Teenagers are capable of all this, but sometimes appear as if they don't because they're so damn caught up in themselves.

Anyway, on to the tricks... At about age 1 kids begin to develop object permanence. Prior to this development children essentially believe that an object out of sight is an object non-existent. A 1-year old may search for a hidden object for about 1 minute, after which time they give up and move on to something else. Here's a video of a great way to trick a 1-year old for your own amusement. This is a nice short video on the topic. The child at the end who looks under the wrong cloth would have watched the adult hide the object under it previously, where he successfully found it. (This is the A-not-B error)

The we have the false belief task. This one is pretty astounding. By this age kids usually have a competent mastery of language, so it seems quite uncanny. They lack the ability to understand that another may know (or not know) something different from oneself. This may manifest in an everday context of a child holding a picture they drew and pointing our features to another and saying something like "...and this is mum, and dad, and the cat" all the while no-one else can see it. In their developing little minds what I know everyone knows.

At about 4 and half kids develop quantity conservation. If you take two equal sandwich halves, but cut one again in half (making 2 quarter sandwiches) and give child A a half-slice and child B 2 quarter slices, they children will squabble over child B receiving more than child A. Quantity is king; as is size. The same goes for liquid - a glass of juice in a tall thin glass will be interpreted as more than the same quantity of juice is a short, squat glass. There's 'more' in the tall glass because it's 'higher', or 'bigger'. The following video shows this nicely - despite the fact that there's only a little difference in the two options, the kid clearly has a preference for the 'taller' container. That look on his face is surprise - he's not made a breakthrough in understanding, it's more likely he's thinking "Holy $%^*, they just made juice disappear!".

Finally, up until about age 7 kids don't understand lies from jokes. That's why it's so much fun to teach them about drop-bears (here in Australia), or perhaps your American equivalent - Tree-Alligators (did I get that right?). You can talk a lot of rubbish to kid of that age and they're never quite sure if you're telling the truth or not....

At any rate, kids are a lot of fun to mess with. These are just a few basic experimental paradigms that establish mental faculties in children over a normal course of development. Believe it or not, many of these techniques are used on chimps and other animals to assess their competence in determining the states-of-mind of others. I won't give this to much a treatment here (Jason Goldman would be a far better choice to elucidate on the topic), but the real trick is testing such capacities without language...

At any rate, enjoy making babies smile; enjoy making yourself smile at the expense of toddlers; and enjoy the look of surprise on the face of children when you can miraculously destroy or create quantity before their very eyes.

If you want further reading look up any developmental psych textbook, or hit me up in the comments and I'll recommend something specific.