The teachers in Yisrael's cheder make birthday parties for the kids- they do it for three boys at a time- the birthday boys come to Cheder dressed in Shabbos clothes, and they give out treats, and they get a present! It is really nice, except that they don't do it on their birthday- so of course, poor Yisrael was
so confused- he knows that his brithday comes after Sukkos, and since Sukkos hasn't come again, he couldn't understand HOW it could possibly be his birthday! So the only explanation I could think of was, "Today is your Arba V'Reva birthday!"