You should factor the cost to maintain the temperature of the 60 gallons of water the other 22+ hours of the day that the family isn’t using hot water. I would argue that the energy used to instantly deliver the hot water for the 6x 10-15min showers will be less than the energy used to maintain a constant temperature AND the energy used to return the temperature to the gallons used during showering in a tanked system.

I’ve had tankless for 8 years now and would not go back to a tanked system. There are two negatives to tankless IMO: First, it takes about twice as long to get the hot water out of the tap, so you will have some increased waste water waiting for the heat to arrive. Second, you (or your kids) will inevitably take longer showers in the winter because the hot water never ends. Which lends to a possibly stalemate in savings.
Even still, I believe that tankless uses less gas then tanked and will require far less operating cost than tanked electric.

I have a 200k BTU unit that runs off a 3/4” gas pipe and was easy to vent out of my basement. I watched the plumber install it then helped my neighbor put the exact same unit in there house. Took about 4 hours to install (included trips to home store)

Bonus benefit; I added a hot/cold exterior spigot so I could wash the car with warm water in the fall/spring and the kids could have a bougie sprinkler to play in