Rav Ovadiah Yosef deals here with two issues concerning modern-day practice on Lag BaOmer - going to Har Meron to give a child his first haircut, and the various other things that take place on Meron on Lag BaOmer.
In terms of using this day and location for a first haircut, Rav Yosef first discusses the idea of davening at the graves of tzaddikim, and concludes that there certainly is support for such a notion, with the motivation issue being that the tzaddik whose grave is being prayed at will appeal to the heavenly court on one's behalf. While there does not seem to be significant support to give a child his first haircut at age three specifically at the grave of Rav Shimon bar Yochai on Lag BaOmer (thought to be his yahrzeit, although Rav Yosef has a footnote which discusses that idea), it nevertheless seems to be a fine and commendable practice.
HOWEVER, in the second part of the teshuva, Rav Yosef basically forbids people from going to Meron on Lag BaOmer. He makes this ruling based on the fact that the scene on that day involves many people dressed improperly and many people shechting animals who probably have no business doing so (and thus the meat is not necessarily kosher). It is therefore better for one to visit these graves on a different day when there is no such scene.