Called their step dad Dad today

So I am divorced from my ex husband and 3 of my kids bio dad. Due to abuse he has supervised visitation with two of them twice a month for 2 hours.

I have been with my partner for 4 years almost, we live together and have welcomed our youngest 5 weeks ago and my partner is fantastic. He is nothing like my ex, he has helped me loads with caring for our daughter, he has taken the kids to school and picked them up, he has done all the visits for them to see their Dad and has taken my boys to all their clubs while I have been getting better (planned c section).

So today we went to our local for a roast dinner, my eldest boy called him Dad and so did my youngest boy.

I have never asked them to, he has never asked them to. They have always just called him by his first name, my daughter who is 17 still calls him by his first name but wasnt prepared for it today.

My partner is really happy that they have called him Dad, but we are taking it one day at a time.