I too think ALL dogs need training. He is still a puppy and needs to be taught the right way to do things. Your son is a toddler, and could very possibly have done something to aggravate Tibbers at another time. You may not believe that or want to hear it, but I'm a mom of three kids and I speak from lots of experience.
When my daughter was about three or four I saw her tap (lightly hit) Sophia on the nose.
I couldn't believe my eyes. I asked her why she did it and she said because she wanted to see what Sophia would do. (My daughter is now 10 and LOVES animals sooooo much...she has a very tender heart for them - she isn't some sociopath or anything.
)
I am a stay at home mom, am VERY attentive to my kids and dogs, and yet this happened. So, my point is, anything could happen. You can't watch your pets or kids every single second of the day.
It's not fair to Tibbers to punish him if he hasn't been given any training. I hope your husband is not being mean to him.
I know you didn't say he was, but from what you said he is saying it concerns me.
I would not freak out about this. Tibbers needs direction and training. And it's very possible that your three year old needs teaching in how to treat dogs.