There are two functions that approximate that: GetWindow() with GW_HWNDNEXT
and FindWindowEx() with the child window handle set to a previously found
window.

However, neither should be used for this, you really do want to use
EnumWindows() (in combination with GetClassName()). The MSDN mentions why
this is so: if anything changes in window ordering or existence while you're
enumerating windows "manually", you're in trouble. EnumWindows() doesn't
have these problems -- this is exactly why we have EnumWindows().

The MSDN contains a useful sample for EnumWindows() under callbacks:
http://msdn2.microsoft.com/en-us/library/843s5s5x.aspx