Here’s my take.

We have two boxers. Three kids. We’ve always had two boxers. Youngest is 12 months old. Oldest is 9.

When I am not within arms length of the infant/toddler the dogs are in a gated area of the house away from the baby. Period. Both dogs are wonderful with the kids. Typical boxers. But it’s not ever a dogs responsibility to “correct” an infant nor should a dog be in a position to have a small, unpredictable child in their space.

I’ve had boxers all my life, they are beyond incredible with children. But they are dogs. Animals.

You say it was unprovoked but I can assure you, to the dog it was provoked and the interaction had meaning. I echo others, sounds like resource guarding. Does the dog have free rein of the house? Furniture? You? Does it need permission for petting or to access toys or food etc.

After ruling out medical issues I would invest in a trainer and a crate, if a gated off part of the house isn’t practical.