That space is pretty small and it's hard to get a finger in there. If it's far enough out that you could, then it's not far enough in to make electrical contact. So yes there can be a 1/4" gap, but your kid would have to get imaginative with paper clips to get to it.
Also, the voltage is half the Euro/APac voltage.
And, if you are at current code, you are likely to have a GFCI or AFCI trip before anything bad happens. We residual-current-detect each circuit, not the whole house, so the refrigerator doesn't quit and food doesnt spoil, and the detection threshold is much more sensitive.
That is the original plug from the very early 20th century... We couldn't change it post-WWII because there were too many NEMA-1 outlets still in service. There were so many because our cities did not get bombed flat in World War II. We also did not get to rebuild our industry, so we were trying to compete in the 1970s with factories from 1933, which worked well for everyone but us. Also, most houses in the city have their original 1910-ish telephone wires, and we now try to push high speed internet over that.
We also did not settle on 220V which means all our appliances are unique to NA, JP, Colombia and Venezuela. Our plugs handle much less power, so we can't have nice things, like a 3000W toaster oven, table saws with guts, or even a window air conditioner that can cool more than one room.
This illustrate those capacities and some of the safety features RedGrittyBrick discusses in his answer.
If you wonder why every American owns a gas lawnmower, it's because electric lawnmowers don't work too well on 120V.
If you really want that style, you can try painting the first 5mm with liquid electrical tape, or slide tightly fitting shrink tube over the pins and heat it with a hair dryer.
Strictly speaking, nothing prohibits you from simply using German style plugs in your house, but you must use the grounded type with GFCI protection in some places, which would be easiest done at the service panel. I like the German style best because the whole plug goes into a recess.