Congrats on the new addition!
Yes I agree it is important to teach modesty. However, it is important also to teach kids that just because something has sleeves doesn't mean it's good to wear. My daughter has a lengthy body so the only
modest swimsuit she's been able to wear is a tankini. I've also allowed her to wear tank tops when she was little and over teeshirts now that she's older. Kids can understand that what was ok for a little kid may not be for a bigger one. They are usually so eager to be adults that they have no problem dressing to adult standards. Sadly, in some families that means baby thongs and padded training bras.
Padded baby bras!!!!!!! I couldn't believe it when I saw that at Wal-Mart. Of course my daughter wanted the super-sized one until I let her try it on (ok I admit it, I was in the mood for a good laugh). Out of her own volition she went and chose one that was much much smaller. Yet when she puts it on she looks like a pair of submarines ready for war (I swear it looked much better in the store). Totally of her own free will that particular undergarment hasn't seen the light of day in months. Like I said, kids are capable of choosing the right when they have the way pointed out for them