I personally don't have a problem with it - people post pictures all the time on Facebook of their summer/vacation photos in bathing suits. Sometimes they're a little revealing and I think oh... but it has to be them falling out of their suits or something for me even to notice!
Are you going to be ok once you send them out? If I've mailed them and then second guess myself, that would suck. Or if my kids voted to not have them be sent - then no. One of my kids would not be ok to have pic like that sent out (at a fussy stage).
As long as you and kids ok with it, go for it! I can't imagine why anyone would have an issue with it! They would like to see their friends/family having fun :)