when things go wrong

My boyfriend and I both have kids. His daughter is 4 and my son is 2. His daughter still dont know whats going on with her parents and she dont understand the circumstances. One night I visited my boyfriend in his house and the daughter was there too. we tucked them in bed and went to his bedroom and had sex. The daughter heard us and talked to him next morning and she is vey upset. She told my boyfriend that "Daddy what did you do with her last night?" Thats not good daddy Papa Jesus will get mad at you. Dont you love mommy anymore ?"  and in that morning I keep calling him to know how they are doing and the daughter was 👍 I dont 👍 her calling you daddy. Why does she keep calling you?" I dont know what to do. Help please. How can we transition kids this age to understand whats going on?