In some cases, it can be appropriate. If they are in a situation where there are no other options due to space constraints and it's a family - only environment, it may be okay. For example, if they are in a small camper van and all the seats are occupied with necessary items.
Well, generally speaking, it's not proper. We should uphold certain social and family norms. Mom and son are family members, but this kind of overly intimate physical contact like sitting on the lap might make both of them feel uncomfortable in a way, and it also doesn't conform to the common sense of propriety in family relationships. There could be other options like sharing a seat cushion or rearranging the seating in the vehicle to make the long drive more comfortable without this kind of inappropriate behavior.
One possible reason could be that there is not enough space in the vehicle. Maybe there are a lot of bags or other items taking up the seats, so mom has to sit on son's lap as a last resort.
Yes, for example, in a family gathering when the son is young, the mom may sit on his lap playfully for a brief moment to share a joke or a warm family story. It can be a sign of a very close and affectionate family bond.
During a family game night, if the son is sitting in a big armchair and the mom wants to be part of the fun. She could sit on his lap while they all play a board game together, creating a warm and friendly family atmosphere.
One 'mom sits on lap story' could be a heartwarming moment when a young child is feeling scared during a thunderstorm. Mom sits on the child's lap to comfort them, and they read a favorite book together. It's a simple yet powerful moment of bonding.
It could be positive. It might be a sign of a close - knit family where such physical closeness, although a bit improper in some views, is just a moment of casualness and shows that they are comfortable with each other.
It could be a rather awkward situation. In the story, perhaps the stepmom was trying to share an exciting view out of the window while on the journey and didn't think about the inappropriateness of sitting on the lap. It could also lead to an uncomfortable conversation later where the boundaries are re - established.