There's nothing wrong with them wearing what they want.
that being said, us men need to watch our emotion of desire so that it doesn't manifest into a problem.
meaning, observe your behaviours around them when you feel aroused etc.
you might find that you're uncontrollable looking too much. when you notice that, keep noticing the urge as well.
nothing wrong with looking. it's a natural thing. but obsessively looking every time is a sign of too much attachment to your emotion of desire

Your kids could have past experiences that would create a false representation of who your new partner is.
best thing to do is to continue as normal with your new partner, and if your children show signs of being emotional (anger, sadness etc) then be there silently until the emotions pass. try not to make a big deal out of it as all emotions pass and the thoughts that are associated with the emotions will pass with them.
resist their emotions and you'll be only helping them hold onto them by suppressing them.
hope this helps