How do I handle this?

I remember when I was pregnant with my second child, worrying about how could I love another child as much as I loved my first.
I spoke with my midwife who gave a lovely analogy. She said, if you light one candle, then take another candle and light it from the first, does it diminish the first candles flame? No, and love is like that, love is infinite.
I've used this for my own children when step-parents and half brothers/sisters appeared and they were comforted by it.

How can you quantify love. It's a feeling. If the little one FEELS he loves both dad's the same that's fine. My youngest was 3 when I divorced and remarried. My husband adores her and she him . She has two dad's and lover them equally. Calls them both dad. My older 3 were 7...11...12 when I remarried. The love their stepdad and their dad. They look on my husband as stepdad but treat him with affection. When he had a cardiac arrest 6 years ago the relatives room was crammed with our children. Our grandchildren are OUR grandchildren. Not step grandchildren. I think the child should be told that's it's ok to love both his dad's equally. It's his choice. Why make him feel guilty. It really is no one's business but his.

Sorry for fat fingers typos

Handled brilliantly, despite very trying circumstances! Take my hat off to you x

Yes - the step dad probably had just given a choc bar or some fun activity or the dad may have just told them off for something or taken their tablet from them or told them to do their homework!
You did well to say you can love someone the same but differently. Its true - we all do.
I love my children the same but differently simply because they're different. Same theory for my gc.
That said I would have been upset too but its possible the next day you gc may have said he loves his dad more.

Take my hat off to you too!
Well done and I hope I would have said the same...although I'm sure I would have felt sad too like you did.