Not shower related but didn't know who else to ask...

Alexandrap

So I had my son's 3rd birthday party this weekend and am now finishing up my thank you cards. My question is I had a few guests who came without a gift, which I doesn't really bother me since I know not everyone's financial is the same but do I also send them a thank you card? Do I simply say something along the lines of thank you for sharing in DS sons special day we were really happy to see you blah blah blah. Or not send a card at all?

Hoping you can help, and thank you.