When 'our' FC said to us that they and their kids 'approved' of us, I was shocked/surprised - it hadn't even crossed my mind that they would be judging us. (In my defence, I was emotionally exhausted from the run-up to intros). Rather than making me feel good, it made me aware of being judged, and I became even more tense than I was before!
I think if they had judged us negatively, my 'who cares what they think' instinct would have kicked in, and it would have been easier (e.g. to pretend).
Ok so there is the 'fake it until you make it' advice, which is valid for your relationship with the child, and which you might as well start now for FC's benefit too...
On the other hand you could also just consistently 'show' how happy and pleased you are, and at the same time strew in little confident 'as everybody knows' or 'as you as experienced FC know' statements referring to how important it is to have realistic expectations, and how different a relationship is when it is 'lived' in every day life, compared to just knowing someone on paper.
But most of all I'd say, who cares what FC thinks about how love should develop. If continuing positive relationship with FC is important for you, then by all means keep them happy - refer to their experience, their professionalism, express thanks, show them that you respect and value what they do - but don't fall into the trap of thinking that you must agree with everything they do/think. Sandwich things where you disagree between two statements of praise if you must, but you are allowed to disagree on some things, and can still have a positive continuing relationship.
But, first of all, focus on the child! If they see you putting the child absolutely first, that alone may make them warm to you.
Good luck with the rest of the intros!