First time seeing my kids in 5 years

I'm really nervous. I just got awarded visitation to see my kids and I'm seeing them supervised next weekend. I was on heavy drugs when I lost custody of them and would leave the house a lot. Their father has had custody for 5 years now. My son is gonna be 18 in 2 months so I don't have a lot of time to make up for everything before he's old enough to decide whether or not he wants me in his life. My daughter is 7 now. She was 2 when their father got custody so she doesn't really remember me at all. I'm trying to figure out how to do this in the most understanding, respectful way possible. My ex told me their mother is his wife and not to overstep. They call their step mom, mom so that does kind of hurt but I understand I need to respect that. She was there when I wasn't and she's the only mother my daughter remembers. Any advice on what to say and do this first visitation?