Thank you notes for a preschooler's birthday gifts: Is it ok if they're a month late or should I not bother?

My daughter had a birthday party with her friends and also the “home” party for relatives about a month ago. I have not sent the thank you notes yet (partly because I was getting professional portraits and was waiting to get them back, partly because I’m a single mother who is out of the house about 12 hours per day, so free time is hard to come by).

Should I send them now, one month later, or should I not bother at all?

Part of me feels if I send them now, I will remind people that they’re so late. I feel like if I don’t send them at all, people will just forget that there was a party (as preschoolers parties are very often at this age).

What do you think?