If i had a son, a daughter, or both, i would get my children to learn woodcarving skills and sowing skills, and get my son to start woodcarving, and get my daughter to get sowing.
I would then allow the mother into the house, and i would ask the kids to huff and puff beforehand, and i would also let them in on the prank.
Then, the mother walks in, hears the huffing and puffing, and asks me (hypothetically) where the kids are. I'll just say they've been in the same room for hours, and point to whatever room they're in. Then the mother might think either " Sex?!" Or " Masturbating... TOGETHER?!?!?!?!"
And then shit hits the fan, she runs in, and there they are, sowing and carving. The perfect prank!
Updated by ippiki ookami