There is a reason that the majority of laws and rules regarding age and knowing right and wrong specify ages around 16-18 as the limit. Ultimately, science and society view that only adults should be held completely accountable for their actions.

Your husband was 10 years old, not even into puberty. Both he and his sister were mentally, physically and emotionally immature so why would you think that their acts would accurately reflect his character at 20/30/40...? I mean if we considered every person who took off their clothes as a child and ran around the house to be an exhibitionist, nudist or pervert....we'd all likely have that label.

I am sure that this memory he has brings him so guilt feelings as an adult, because viewing the situation from adult eyes...he feels he did something wrong. The thing is...as a child, there was nothing wrong. As children, we are all innocent....we are curious, we explore...we experiment, we get hurt. In this case, no one got hurt and the two were likely curious about what made each other different.

I think that your husband needs to work on removing the guilt he seems to be feeling, as it is likely a bit unhealthy. He shouldn't apply adult morals and judgements to events at 10 years old. He needs to work on accepting his childhood, with all the experiences that it included.