Distracted Spanking

After church on Sunday, my husband Jack was giving our girls, Olivia 14, Erin 12 and Kim 11 their spankings. When Jack was finishing up with Kim, Olivia and Erin were talking and giggling together. I asked them what was going on. Erin spoke up first. “When Daddy was spanking Olivia, he had a lump on.” I never heard that term. “What do you mean, Erin?” “You know, Mommy, in his sweat pants, he had a big bulge. My friend said that is called a lump on.” I had to stifle a laugh to remain serious. “Honey, the correct term is hardon.” Erin had this mischeivious look on her face. Obviously her friend had told her more details. She looked up at me. “But what does it mean?” I brushed her off. “Honey, it just happens sometimes.”
At 14, Olivia is developing nicely. At 12, Erin is becoming shapely too. Obviously, Jack is becoming aroused when he spanks his pubescent girls.
My question that I need advice on: Is it common for Dads to get an erection when they spank their daughters bare bottoms? Do I need to be concerned? Should I take over all the spanking myself? And honestly, I’m not immune to the beauty of their bare bodies either. Is it time to cover up for spankings?