I was a single parent, and in the first grade, my daughters class made Mothers Day cards. She gave the one she made to me. I still have it. She still sends me Mothers Day cards. Sure, it's not what would normally be expected, but do you think that matters to either of us? As long as the parents and kids come to terms with the situation, it's nobody else's business.
That's fine, but you wouldn't call yourself married, nor would you call yourself your daughter's "mom and dad". This isn't about what's adequate; this is about what is married.
then why are you talking about mom's and dad's?