How to deal with parallel edges between two vertices in cycle detection using BFS in an undirected graph?
If the case arrives where you see the case of a node being already visited but it is the parent of your current node, you just have to check whether there is a double edge between them. How to do that depends on your data structure, but if your adjacency list is sorted it would just amount to searching for the edge and checking how often it is in there.

Another problem I see is that your adjacency list doesn't actually contain any information that the edge is doubled.

For directed graphs, you can just completely get rid of the "parent check", as the only time that case arrives is when you have two edges going from $u$ to $v$ and vice versa.

Additionally, be careful if the graph is not connected, your BFS will not cover all of it, so you would need to start another BFS from an unvisited vertex again. This is especially important for directed graphs, as even if the graph might be connected, your BFS will probably not cover all of it.