Sky's mother keeps disappearing and reappearing (coming back). No wonder hide and seek is so much fun!

During their first year, however, babies will learn an important concept (idea), which is object permanence: objects still exist even if we can't see them.

When babies are Mia's age they know they have to look for an object, but they might not have everything else straight.

Ten-month-old Simon is about to make a very common mistake. Although he watched us place the toy plane under the white cloth,

he'll look for it where he last found it, not where he watched us hide it.

Woman: "Can you look at these two glasses. Do you think they have the same amount of juice in them?" Girl: "Yes."

Woman: "OK, now we're going to pour this juice into this glass. Now tell me which glass has the most juice in it."

This time, the child chooses the tall glass because the tall glass appears to have more juice in it.

In this example, the girl is asked which row of coins has more coins, or whether both rows have the same number of coins.

After counting the rows, she then says the rows have the same number of coins: "five coins in each row".

After the woman changes the coins, the child is asked again which row has more coins.

She chooses the first row and says it has more coins because there is more space at the beginning of the row.

The spacing between the coins makes the row appear to have more coins, making it look longer then the other.

In this third example, the child is asked if they have shared the biscuits fairly and equally.

She says no, because the woman has two and she has one.

After the woman breaks the little girl's biscuit in half, she is asked if this time they have shared the biscuits equally.

She says yes, they have, because now they both have two biscuits.

Woman: "Can you tell me what you see, when you look at that from where you are sitting?"

Boy: "I see a cat and a tree and a barn." Woman: "OK, now we are going to do the same thing."

"Can you tell me what you see when you look at it from that side?"

Boy: "I see an owl and a goat." Woman: "Is there anything else that you see?"

Boy: "A tree, and another little tree."

Woman: "Can you tell me what I see when I look at this from where I am sitting?"

Boy: "An owl, a goat, and a little tree and that and that and that..."

The woman asks the girl if she thinks there is the same amount of juice in both glasses. The girl says there is the same amount of juice.

The woman then takes a long glass and pours the juice from the short glass into the long glass.

She then asks the girl which glass has the most juice. The girl says both glasses have the same amount of juice.

The girl also says that just because the glass is tall and skinny doesn't mean it has more juice.

She says the tall glass has the same amount of juice, it's just that the short glass is wider (fat).

Woman: "If you hit a glass with a hammer the glass will break." Then the boy says he knew that.

Woman: "Then this one says Don hit a glass with a hammer." Then the boy says he knew that too.

So the woman asks what happened to the glass, and the boy says it broke, and it broke because the hammer is hard.

Woman: "If you hit a glass with a feather, the glass will break." Then the boy says, "No, it won't."

Woman: "This one says Don hit a glass with a feather, so what happened to the glass?" The boy says "Nothing happened."

Then the woman asks, "Why will nothing happen?" and the boy says, "Because the feather is soft."

Woman: "The rule is: if you hit a glass with a feather, the glass will break."

Woman: "The second one says that Don hit a glass with a feather. What happened to the glass?"

The teenager says, "The glass broke. Because the rule says, 'If you hit a glass with a feather, the glass will break'."