Confidence is a huge turn-on for both men and women. I agree that you should approach guys as well and not just wait for guys to approach you. It will boost your confidence level (seeing the reaction you get), which in turn should increase your being hit on by guys.
There could be some issue with your body language (i.e. putting off some form of "stay away" resistance even if you don't mean to), but without video of the event, I couldn't say for sure.
I would also caution you not to look for dating partners at a little boy's birthday party. It is quite possible that the guys there thought it was in a little bit of bad taste to make a move on a woman at a little boy's party.
Good luck.
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