>The Individual Values of the parents actually influence the IVs of
the child, to some degree. 3 of the 6 stats are based on the
parent's IVs, the rest are chosen at random. So, for example, if you
are breeding a Volbeat and Illumise, the male Volbeat may give it's
HP and Sp Attack IV, and a female Illumise could give it's Speed IV.
Each parent will contribute at least one IV, though.
It's pretty much the same as any generation. How is it not completely though? Because Destiny Knot didn't exist then. 3 IVs from both parent's IVs is good, but it just isn't good enough. The rest of the 3 IVs are completely random. So even if you were to breed two 6 IV Pokemon you are only guaranteed 3 perfect IVs on the offspring.
Your best bet is to keep trying and press on, IV breeding is not easy in LeafGreen (at least compared to the later games). Try two Pokemon with at least 3 good IVs each. Good luck.
Hope I helped!