What age group is this costume for?
Elementary School
Middle School

Estimated time required to make this costume:
About half an hour, depending on your creativity.

Difficulty level:
Quick and easy - no sewing required

Items you will need: (Hit your return key to start a new line)
Bug Costume (any type)
Top Hat
Millenium-Related Paraphernalia

Instructions:
Decorate the top hat with sayings like "Y2K", "Millennium", "2000", etc. Then, have the child wear the bug costume and tell people that s/he is the millenium bug, Y2K! This is cute and funny.

Other information to consider:
You may end up buying a bug costume if you aren't creative enough, but that is OK. Try to rent one or get a really cheap one. The point is the Y2K, not the bug aspect.