"I am hoping to find a Lenten activity that includes parents and their children. It needs to be a brief learning session that can be done within the timeframe of the children’s formation classes. Any suggestions?"
Prepare catechists by telling them that they will not have the children for a full class on a particular day. Let parents know a couple of weeks in advance that you would like for them to meet in the gym (or another large meeting space) so that you can talk about some Lenten information and have parents and children together. You will probably want to deal with only two or three grade levels at a time so you can customize your vocabulary for presentation. Do the other grade levels on another day. One of the most informational and helpful sessions would be to present some catechesis on what the scrutinies are and what an exorcism is. The liturgical reality of these terms will be played out during three of the Sundays of Lent. Most people, even those who have heard them before, have no idea what they really are.
Tell the parents that during Lent they will be participating in the celebration of the scrutinies which will address a spiritual purpose of self-searching and repentance for the candidates and catechumens who are preparing to receive sacraments at the Easter vigil. There will be catechesis during the liturgy which speaks of sin and our need to repent; there will also be mention of the devil. These are realities we must all face in our journey of holiness. At one point the celebrant will mention the word “exorcism.” The need to exempt the devil from our lives is a very real challenge. This does not have to do with the occult but very much has to do with our Christian need for dealing with sin. This is also a good opportunity to mention to parents and children that this is a good time for them to consider receiving the sacrament of penance (reconciliation) themselves so that Easter can be truly special and joyful for them.
The session should only be about fifteen minutes long. There may be lots of questions from adults who have never had this explained. Dismiss the children to their classrooms with their catechists and make yourself available to answer questions that parents may have. You can choose another topic but be sure it is something which they will experience soon so it seems more relevant to both children and adults. You might want to do a session on the Holy Thursday liturgy so folks are prepared. Holy Thursday is actually one that is good for even grade schoolers to attend because there are different things they will experience which they can understand.
For those of use who are involved in ministry, we sometimes take for granted that others understand about things that happen in church. Yes, the liturgy speaks for itself, but many of the rich symbols and rituals that are present are not in their frame of reference (they never use a candle to light a room, infrequently experience a family meal, do not use oils for healing, etc.). Lent is a teachable moment. Grab it!