James Akin says Polygenism is not irreconcilable with Catholicism..
When Pius XII dealt with the subject of evolution in his 1950 encyclical Humani generis, he didn't treat the question of polygenism (the idea that there were more than two individuals at the dawn of humanity) in the same way he treated other aspects of the question. He hedged his bets a bit on this subject.
While he said that Catholics did not have the liberty to advocate polygenism, he didn't say that the reason for this was that polygenism was totally and irreformably unable to be reconciled with the sources of Catholic dogma. Instead, he said it was because "it is no no way apparent how such an opinion can be reconciled with that which the sources of revealed truth and the documents of the Teaching Authority of the Church propose with regard to original sin" (HG 37).
This leaves open the possibility that a way of reconciling polygenism with the sources of dogma might eventually be found. Since his time many Catholic theologians have conjectured that there are ways in which polygenism can be reconciled with original sin (e.g., saying that Adam and Eve represent the early human community which as a whole turned away from God at the beginning of our history and thus committed original sin, passing it on to us).
A number of years ago the German conference of bishops published A Catholic Adult Catechism that was published in English back in 1987 by Ignatius Press. This catechism contained a section on evolution that said it was possible to reconcile polygenism with the Church's teaching if certain points regarding original sin were maintained. I am also given to understand that this Catechism was also reviewed by the Vatican (after the debacle of the Dutch Catchism), which did not mandate a change in this section.
It is further to be observed that, in John Paul II's statements on evolution (such as the famous speech to the pontifical academy of the sciences) he is quick to reaffirm all of the things Pius XII said about the limits on how evolution is compatible with the Catholic faith except on the subject of polygenism, where John Paul II said nothing at all.
JP2 was not saying that it's okay for Catholics to go ahead and advocate polygenism, but he was conspicuously silent in reaffirming his predecessor's stand on this issue and may have been holding the door open for one of his own successors to revisit this issue and take a different position.
It is possible that, one day, a pope may issue a new statement on evolution and say that a way has been found to reconcile polygenism with the sources of faith.
But that hasn't happened.
The Catechism of the Catholic Church continues to speak of Adam and Eve in monogenistic terms, and there has been no Vatican declaration on any level (so far as I know) that polygenism is compatible, but there is a greater degree of reserve shown by the pope on this subject in recent years, and the Vatican has let pass local magisterial statements--like that of the German conference of bishops' catechism--that displayed openness to polygenism.
If you're teaching a bunch of school kids, I wouldn't go into all this with them. It could well interfere with what their parents want them to be taught, and parents have the ultimate say in such matters. But for your own benefit you may want the additional background as a way of gauging the degree of firmness that the Holy See is presently placing on this topic.