For the record, DH and I are TTC #1, so we haven't hit this yet. But, while we were in Europe this summer, this came up because its just a part of life over there. You don't have to seek out places, you just go to the public beach where there will most likely be quite a few topless and every once and a while completely nude adult and A LOT of completely naked children. (On a side note, one of the cutest things I saw in Europe was this little 2 year old girl, naked except for her shoes, running along the promenade in front of her parents who were taking a break from the beach to get an ice cream! So cute... would have loved a picture for cuteness sake, but that is inappropriate, so I didn't). In fact, the majority of pre puberty girls are just in little bikini bottems.
I went with the topless thing and would do so again in front of my future kids without thinking twice. In fact, we will purposely try to include beach vacations in Europe just to allow our children to be comfortable either way... its a nice mix and wonderful to see soo many natural bodies instead of the sexed up stuff we see on American beaches. I'd like them to be able to see a man in a speedo (or completely nude) and not go "yuuuuccckkk". (On another side note, I was amazed how few augmented breasts were in Europe... even though US public beaches aren't nude, man alive, I'd be embarressed to let my kids see some of the women in their tiny "tops" all augmented to timbuckto...talk about giving the wrong impression.)
I'm not sure I would seek out a nudist club only because I'm not sure its worth the effort seeing as we do frequently travel to Europe and I would be a little concerned about pressuring my kids to be nude. I think the whole point is to allow them to be tolerant and to be themselves... so to go to a nudist club where it is mandatory may be to pushy for me. A mixed club would be perfect, but I'm not sure how available those are in the US.
And for all you naysayers... how do you think you allow breasts to be less sexual and more about breastfeeding? There are many that believe seeing them as natural instead of covering them up is a big step towards that.
As far as tips: bring sunscreen and lots of it.
Oh, and taking them in Europe where it really isn't a choice is a nice way to avoid the whole "seeking it out" think w/ my conservative family... but I realize not everyone has those options (or a conservative extended family!)