I was supposed to/I was going to/I should have

[Topstudent]

A: Did you see your kids over the weekend?

B: No. I was supposed to see/was going to see/should have seen them, but I got sick.

If there was a mutual agreement between B and his kids about seeing each other over the weekend, which one of 'was supposed to see', 'was going to see', and 'should have seen' would make most sense and be most natural here? Thanks.

 

[jutfrank]

was supposed to