Okay kiddo, do you remember Passover? It's a Jewish holiday where we remember when our ancestors were slaves in Egypt, but they got freed because God helped them.
Well, after Passover, there's something called Pesach Sheni. It means "Second Passover."
Sometimes people couldn't celebrate Passover on the right day because they were sick, traveling, or busy with something else. So God said they could celebrate it a month later on Pesach Sheni instead.
It's kind of like when you have a make-up test at school because you couldn't take the real test on the right day. Pesach Sheni is like a make-up Passover.
So, that's what Pesach Sheni is all about - giving people a second chance to celebrate Passover if they couldn't do it the first time.