I tried it (the pause trick) as well, and thought it had failed. But while trying to put all my kids where I thought the mushroom was (maybe it was just invisible?), a new collectible suddenly appeared... IN PAUSE MODE!

So I very quickly grabbed about 5 kids and put them on it and then unpaused the game... BINGO! 500 tech points in one fell swoop. I assume, if an item can appear in pause mode, it can also just as easily disappear. How long does an item stay around? Anyone know?

Knowing this, I suspect you could rack up quite a few tech points, scrolling around in "pause mode" waiting for a collectible to show up, dumping a ton of kids on it, and then switching the game back on.