If you were learning a musical instrument and you only did the lessons once a week, with no practice in between progress would be really painfully slow.
Judging by the amount of people we pull out of the sea each year, I would say the british don't take swimming very seriously.
Most people end up at a remedial standard at best, which doesn't really give them a fighting chance, and certainly means a whole host of water sports are not going to be accessible to them.
We live on a planet with about 74% water, at some point you will really wish you were a stronger swimmer, it's hard to avoid.
start swimming lessons and keep going, and then add a swimming club, make your children swim laps at least twice a week, from about 9, one day they will thank you,
get them sea and river smart, make sure they do courses on the sea (kayak,surf,sail), learn about rips, tides.
I've lost count of the amount of people I have gone in for, I've lost count of the amount of children I have pulled out who's parents were not able to rescue them themselves.
rnli.org/aboutus/lifeguardsandbeaches/Pages/Lifeguards.aspx
join the RNLI, rase money for the RNLI, save your own life.