Kid (2 1/2) is really obsessed with whether I am happy. And he alters his behavior based on it. It's very tempting to use this, of course. But, I don't think whether mommy is happy is the best way to develop moral character. And I don't want him living his life based on whether I am happy.
But...I don't want to deny that I have emotions. And no, I'm not happy when he throws the contents of his piggy bank all over the living room. Or more serious stuff, like kicking me.
I usually try to say things like, "I'm not happy right now, but I love you whether I am happy or sad." or "Yes, I am happy now. I had a great time playing with you and your friends. And I love you even when I am happy or sad or mad."
Anything else I should be doing or saying?
I think in the context he means it, I don't know that wether or not you love him enters into it and may only be more confusing.
I think it sounds like he is developing empathy and a recognition that other people have feelings. So "No, I'm not happy, your kick hurt me" or "I don't like cleaning up big messes" is maybe pretty valid framing for this age. I've always been pretty clear with my kids "I am really fustrated. You dropping that pitcher of juice after I asked you not to touch it made a big mess and now I have to clean it up." Maybe I'm screwing my kids up though... i don't really know :P
My 2.5 year old asks me this all the time. I just try to respond as honestly as I can, for example: "Mommy is not happy right now because you just bit me in the head." I usually don't have the presence of mind to tell her that I love her at that moment, but it would be a good thing for me to keep in mind.
Sometimes, if she's been misbehaving a lot in one day, reminding her that I still love her can catch her off guard and make her calm down a little. I think that goes back to misbehaving to get attention. She's been doing that more often lately, especially when her little brother needs my attention.
My 2.5 yo definitely gets it if we're happy or not. I definitely tell him if I'm not happy because he threw a block at my head, or I'm happy he helped put toys away. A couple weeks ago I was having a weepy day and he noticed and came over to cuddle and gently patted my head and said "It's okay mommy, don't worry". I love seeing that kind of empathy in him and encourage it. Or, when he hit daddy in the head (kind of on accident) with the eyeball of a stuffed animal and it left a mark. He brought his toy chainsaw over and told daddy it would be okay, he was going to cut his boo-boo down.
Basically I just interject the happy/not happy statements into our daily routine. And I say a lot of "I love you"s at random times.