twins fighting

[Amanda+2]

just thought I'd ask a quick question.by b/g twins are 3.5 and they are starting to get a bit physical in their fighting. quite happy to hit/slap each other. and apart from crying to get attention from me it doesn't seem to bother them. they don't hit other kids just each other.

obviously they go into time out etc, but generally speaking they both have to go in at the same time because they both have hit. i have no idea how to deal with it, our whether to 'ignore' it as it does seem like an extension of their closeness

any ideas?