I wouldn’t agree with your wife’s views on this topic because 6 is quite an age for children to remember such incidents. I myself remember some strange (then) incidents that have happened when I was young, like older women changing in my presence; so I advise you avoid this and take care to see to that it doesn’t happen again.
Even thought the sexual awakening doesn’t happen in this age, it is quite possible that your elder son might remember seeing his mom naked when he was young. They surely wouldn’t feel anything watching your wife naked right away but they might remember seeing her naked in their older ages, so avoid this or at least send them out when you need to change.
It doesn’t quite leave a positive image for your elder son, so try to find an amicable solution to this. Send them out when either of you have to change; as for making love, I guess your situation is quite not changeable because your house is small, so that doesn’t give you the privacy you need with your wife. Never assume that your children are sleeping and be careless. You never know what they actually are doing, so take reasonable care while making love.
Try to make love when your children are not around, say on your off days in the mornings when you can send them out of the room, or some other time when they remain outside with other members of your family. Avoid making sounds or for that matter any movements that would give out what you’re doing. They clearly do not know what you’re doing but they wouldn’t just leave it out, so take proper care. On weekdays, try to keep your session to mere penetration while on the weekends when your children remain outside the room in the mornings or anytime other than bed time, quench your desires. It is a tough ask, but you should make the best of your living in some way and I think this is one. Good luck.
