Well, I have a disgruntled reader who challenged me as to how I can determine whether a Mass is invalid or not. This is not rocket science.
Firstly, there is a difference between invalid and illicit as terms. The Eucharist, which is a sacrament, is what is valid or invalid. The Mass can be licit or illicit.
Let me quickly run through both types of definitions.
A Sacrament of the Eucharist is invalid when: 1) the priest is not validly ordained-invalid orders or no orders, like women priests and Anglican priests; 2) the words of Consecration are changed or when the hosts and wine are not consecrated at the same time-invalid form; 3) the intention of the priest is to separate from Rome or his intention is not to obey Rome in matters of the Eucharist; that is, he does not believe in Transubstantiation or he has purposefully separated from Rome, as with the Anglicans-invalid intent; 4) invalid matter-not bread and wine, but rice cakes and grape juice for example.
The Mass is illicit, that is illegal, 1) when the priest does not following the rubrics for the Mass; 2) when the place of the Mass is not canonical-such as on a beach or at a picnic (or in a home without permission of a bishop); 3) when the priest does not have faculties to say Mass or is suspended. There may be more reasons.
There are also rules against ceramic altar ware. No pita bread or honey breads.
Can. 924 §1. The most holy Eucharistic sacrifice must be offered with bread and with wine in which a little water must be mixed.
§2. The bread must be only wheat and recently made so that there is no danger of spoiling.
§3. The wine must be natural from the fruit of the vine and not spoiled ...
Can. 926 According to the ancient tradition of the Latin Church, the priest is to use unleavened bread in the eucharistic celebration whenever he offers it.
It is easy, when attending a Mass and when one is listening carefully, to determine if the Mass is illicit and the Sacrament invalid.
All parents should be aware of these rules and act on them accordingly. This is not hard to do.
Council of Trent, Seventh Session March 3rd, 1547: Canon 11:
If anyone says that in ministers, when they effect and confer the
sacraments, there is not required at least the intention of doing
what the Church does let him be anathema