You would die, of course. But your child already knows that. They want to hear about the specifics. The details of the next few seconds of your life are indeed fascinating, even to an adult. Your child may realize the lack of air as being the enemy, but that’s actually third on the list of fatal environmental conditions. You would  suffocate (eventually), but before that happened the fluids inside your body (blood, water, etc.) would boil due to the zero pressure of space. That means that within the first 30 seconds, your skin and tissues would puff up and expand rapidly, like foam coming out of a shaving can, until they ruptured all over your body, inside and out. But then as soon as your cells and blood finished boiling/exploding, they would instantly freeze in the extreme cold of space. This would all happen in less than a minute. So if you appeared in space without a spacesuit, you would swell up, explode, then freeze, more or less simultaneously. Tragically, there wouldn’t be much time to suffocate.

Your child may want to know about all three of these deadly forces individually, so here is how each of them would kill you:

1. Zero pressure –  your blood and tissues would boil instantly, and your lungs would rupture in just a few seconds. This is similar to “the bends” which can happen to SCUBA divers who ascend from deep water too rapidly.

2. No air – space is a vacuum so you would eventually suffocate. And if you took a big gulp of air just before you entered space, that would make things worse as your lungs would explode immediately from internal pressure.

3. Extreme cold – the exact temperature of space is debated, with estimates saying deep space is approximately  -450° F  (absolute zero) to about -200° F within our solar system (the sun keeps it a bit warmer). So after you passed out and exploded, whatever was left of you would most likely freeze into tiny crystals floating in space. Could you vacuum up those crystals and thaw them in a microwave? Yes, but you would be left with a big pile of goo, not a human being.