One last point: Genital Warts usually show up in the months following exposure. The fact that this happened a year ago, and your children are wart free, is yet another indication that there was no transmission.
HPV infections are usually temporary. Most people clear the infection within months, with few having active infections for more than 2 years. The fact that the warts have gone away on their own suggests that the virus has been cleared, and he can no longer transmit the infection.
Genital HPV is almost always sexually transmitted because the virus must be massaged into the skin, usually through small breaks in the skin caused by friction during sex. It is unlikely that the virus would be transmitted through casual contact, and also unlikely that your children would get the infection in areas not covered by clothing. Furthermore, a bathing suit will cover all the areas most prone to genital HPV infection. Genital HPV infections do not seem to take to legs and stomach all that well.
With this in mind,the chance of your children contracting warts this way is close to zero.
Probably not an issue at all.
First, genital HPV infections have to be "massaged" in....so they are almost never transmitted through casual contact. It usually takes sex.
Secondly, genital HPV infections are rare outside the genital area. Are you sure your husband has genital HPV on his stomach? Even if he does, it is unlikely that genital HPV infections will transfer to your child's legs. HPV does not transmit through clothing, so the bathing suit will protect all covered areas.