When do boys develop the common sense gene?

[Dobie]

I nanny for a family a few days a week that has 4 kids. The older boys are 7 and 8, Domenic is 18 months, and the little girl is 12 weeks (she was born 10 weeks early and still needs a lot of care)

So I go over there yesterday, and send the 2 older boys in the back yard to play after school. I tell them I'll call them in after I feed the baby and give Domenic his bath, I tell them we'll make brownies. Now, any other day, they will come in 30 times in 30 mintues either tattling on each other or asking for a drink. So, I KNOW they know how to use the back door.

I feed the baby then check on them, eveything's fine. Run the tub and check on them, everything's fine. I put Dom in the tub and let him play for about 20 minutes - I can't leave Dom alone, so obviously I can't check on the older boys, but it's a fenced in yard and I KNOW they know how to use the backdoor and come inside if there's a problem.

I finish Dom's bath and get him dressed - we walk into the living room and I glance out the front window. IT's POURING OUTSIDE!! With the bathwater running, I hadn't heard it in the bathroom. I go to the backdoor and see the 2 boys standing in the middle of the yard, shivering, soaked to the bone and just stareing at the door. They had their little hoods up and water was dripping into their faces. I don't know the words to use to describe how pathetic they looked. So I said - "Come inside, it's raining, why are you just standing there looking at the door". They BOTH burst into tears and start yelling "YOU DIDN"T CALL US IN". So basically, they know how to use the door to come inside to tattle, ask for something to eat or drink, use the bathroom, ask if we can go to the park, or a million other things that they want to do - but if it's pouring out, they NEED me to tell them to come inside.
AT what point do boys develop that common sense gene?