For me, I did role plays with my own children. I told them about not keeping secrets coz some secrets can be bad. I told them some touches are necessary such as bathing but some touches that made us feel uncomfortable, are bad touches. We did role plays such as on crowded bus, playing, etc and whether they feel is good or bad touches. Then explain. Before that, I taught them where are the no no places for others to touch on our body. I also role play on what to do, if such thing happens. It is interactive and fun so try it.
You may find this article useful: http://www.healthhub.sg/live-healthy/376/protect_your_child_sexual_abuse The important point would be to let your children know that he/she has to inform you if they are being touched by someone else who is not you or your husband.