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This Q came up while talking about black holes with family: What if an asteroid was heading towards the Earth, but it was so high density that it's a tiny black hole so we wouldn't see it with telescopes? Also what does it look like when a micro black hole asteroid hits a planet?
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The Chandrasekhar limit for white dwarfs is 1.5 M☉, any greater black hole / neutron stars can form. Asteroids vary in size, but plugging it into Schwarzschild radius equation gives us a size of r_s = 3GM☉/c^2 so I guess that could be asteroid sized.
I cba to check if r_s = 3GM☉/c^2 is in the order of magnitude of an asteroid. But that covers most of your child’s questions about black holes.