From the Sources
When Hashem promises Avraham that he will have many children, he says that his descendants will be as numerous as the stars, if they are meritorious and, if not, they will still be as numerous as the grains of sand in the world. In fact there is a wonderfully exciting (especially for children) explanation which says that Hashem actually took Avraham into outer space in order to see the stars. This is because it says that Hashem took Avraham outside to see the stars, and that it only became dark only AFTER Avraham saw the stars. The idea is that he was taken into outer space so that he could see ALL of the stars whilst day was still day.
How to eat it
Okay so several options here. Make the “crumble” part of an apple crumble, and serve is with sliced star fruit. Or candy stars if you can find them. I think a lot of kids would also find it VERY exciting to make a spaceship cake.