Ever since Jack was about 4 months old he would suck on his last three fingers when he got tired and it would put him to sleep. Now that he is running around like crazy non-stop this is the sign we get when he has had enough fun for the day. It doesn't matter where he is at...maybe on the swings, in his high chair, or mid run- when he gets tired he stops what he is doing and those finger are in. His fingers will go into his mouth and not come out until they are exchanged for a bottle of warm milk. It's quite precious.