If you think experiencing pregnancy and newborns back-to-back would be the hard part, a new story from Jessa Duggar Seewald is cause to reconsider. As the mama of two boys who are just 15 months apart in age can attest, keeping her two toddlers safe from each other is no small task.

One recent experience in particular had the Counting On star asking the question just about every mom of a toddler has asked herself: "How can 2-year-olds be so cute and innocent, and yet such little stinkers at the same time?"

Recalling the incident from this week in hilarious detail on Instagram, Duggar explained she had to employ some serious "mom detective" skills when she suspected 2-year-old Spurgeon was lying about how 1-year-old Henry got injured. It started—as most of these things do—when she was momentarily away and heard Henry "whimpering" from the other room.

At first, this wasn't much cause for alarm. Apparently, a certain toy fire truck has been causing lots of disputes between the two boys, so Duggar assumed they were yet again arguing about whose turn it was to play with the toy. And by the time she arrived on the scene, her older son was "lovingly" helping his little brother and explained that Henry "hit head."

"I didn't want to assume anything since I hadn't been a witness," Duggar says, adding Henry is "in that clumsy toddler stage, so he is always taking little tumbles or bumping into things. I picked him up, and he was perfectly content again!"

That's when the story could have ended—had it not been for what Duggar noticed later while nursing Henry before his nap. "I brushed his sweaty hair back from his forehead, and that's when I got a glimpse of this: little red marks in a perfect circle, with a line down the middle. Immediately, I thought 'Tail light.'" (Slide over for the picture. How funny is it that she was instantly able to identify the mark as one from a tail light?!)

Duggar explains that as a "self-proclaimed toddler psychologist," she was able to get a good sense of what probably happened: She suspected Henry was trying to steal the truck from his older brother, which caused Spurgeon to wield the toy as a weapon and "bonk" his brother on the head. Then, when Spurgeon saw how that upset his brother, he switched into "consoling and comforting mode"—which was when their mom arrived on the scene.

Although Spurgeon wasn't caught red-handed, the red fire truck backed up Duggar's hunch: "I confiscated the evidence (aka: toy fire truck), and... it was a perfect match."

Duggar didn't explain how she handled it from there, but did give credit to her younger sister Jinger Duggar Vuolo for bearing with her when she was "THAT KID." As Duggar adds, "This gives me confidence that my boys will continue to be best friends forever."

With 18 siblings of her own, Duggar knows what she's talking about there!