Golf the smallest circle!
Wolfram Language (Mathematica), 28 27 bytes

#~BoundingRegion~"MinDisk"&amp;


Try it online!

Built-ins are handy here. Output is a disk object with the centre and radius. Like others, I’ve found the 2nd and 3rd test cases to be different to the question. 

Thanks to @lirtosiast for saving a byte!

If a list is required as output, this can be done in 35 bytes (at the cost of an additional 8 bytes). Thanks to @Roman for pointing this out.