OH NO...Don't delete them!!!! there's no reason to do that. Just be careful where you post and use them. It's just a good idea to get the A-OK before marketing with them and the like. I'm pretty sure you would be doing no harm posting on tpf for some advice on taking the picture. But for instance, I threw together a direct mailer with a couple of event pics. I made sure to get the ok's from all parents whos children appeared on it (I had no contract with them, more of a freelance event with the approval of the head of event to take the pictures). I think too its just good practice that at the minimum the parents are aware of what you are doing with the picture. Regardless of right or wrong, if the parent doesn't want anything done with the picture it would behoove you to respect their wishes.
With all this being said, you may want to consider getting the consent from the association of (youth baseball in that town?) if you are looking to sell pictures. I'm not sure of the legal ramifications of not having it though. A lot of times they already have contracted photographers working the events.
But all in all, there is no need for you to delete your pictures.