The 'pause technique' is trickier on an iPhone or iPod touch, since keyboard input is not implemented (in the desktop versions, pressing the space bar pauses and unpauses the game). Since putting multiple children on collectibles isn't officially supported, you'll have to see if the technique works for you.

If you want to try it, you'll need to go to the menu screen, tap Options, pause the game, then return to the game. Put multiple kids on the collectible, then return to the options setting and set the game back to a non-paused game speed. When you return to the game, watch what happens to see how many children picked up the collectible.