I created a custom list in a top level site of site collection, which is the parent site. Is it possible that this list is visible in a child site?
There are different ways for doing this, a simple method could be to export the listview webpart of the list from the parent site. Open the exported .webpart file and set the WebId property of the parent site since its set to 00000... Then finally import it to your subsite.
A quick search should send you in the right direction, alot of topics on this. E.g: http://blog.pathtosharepoint.com/2009/01/22/a-simple-method-to-display-a-list-in-another-site/