Could it just be that you're not noticing? I guess it depends too on whether he/she is very active. Maybe he's just chilling out in there. It could be possible that he's more active at night whilst you're sleeping and when you're awake you're not noticing because you're preoccupied with the other children etc.

Try drinking an icy drink and have a lie down if you can to see if that gets him/her moving.