when i saw this little boy (i think?) i thought "kiekeboe". of course, wikipedia has an entry about kiekeboe (here), and this is what they say: it is a game you play with babies between the age of 6 months and 2 years. you try to get the attention of the baby, and then laugh; this will make her or she laugh back. then... you hide your face (behind your hands or whatever), and after a few seconds you "come back" while saying "kiekeboe!" the baby will be surprised and laughs again. it is thought that such little kids really think you are gone when you hide your face, and they are surprised when you show up after a few seconds. as such, you can do it over and over again, and the baby will be surprised each time.... supposedly, it is a good way for the baby to develop face recognition.
now, im just disappointed that wikipedia does not tell me how this game is called in other countries. so... anyone? i cannot imagine its something only dutch people do.. :)