Anyway, this is a great song for teaching ta rest for your 1st graders, or bringing it back later on to practice low so. I wouldn't really use it to present that, because the interval is always re-so, but it would help enforce I-V accompaniment, and is really good for practicing that interval.
Latin American folk songs often have an uneven feel to them, because a lot of the time, their phrases are a little uneven - just different from what we're used to here in the good old U.S.A. This song has that uneven phrase thing - sort of. It has 4 equal-in-length phrases, but each phrase is 6 beats long. That's a little unusual - but cool. Something that you can point out to your kiddos! The form is ABA'B - so it's great for pointing that out as well.
OR, you can wait until next week, when I'm throwing a big Cinco de Mayo sale and get this for 20% off, as well as all of my other Spanish language files :)