I know your girls use safety stirrups. But I have said this before - I would not let my own kids or grandchildren ride like that with their feet pushed so far into the stirrups.
Show them some pictures of Michael Jung jumping. It isnt just safety and balance - With the tread of the stirrup under the ball of your foot, your toes and ankle joints are very free to move. We were taught that way, with it one of the basic foundations for all of us learning to ride. We were expected to be able to spread and wriggle our toes, when sitting, rising and in forward seat. It is on my agenda for January as I discovered to my chagrin that I cant ride Grace standing in my stirrups. Not clear whether this is due to my being ten years older or my not trusting her as I trusted Maisie.
But your girls havent altered a bit over the last two years.