The silence was observed by public bodies including Sefton Council and Merseyside Police.
The force said it was pausing “to remember the light, the kindness and the joy that Alice, Bebe and Elsie brought into this world”.
It added: “We will never forget that day or the impact it has had on those whose lives were taken, their loved ones, those who survived, and those who responded.”
People were encouraged not to leave floral tributes but instead to donate to local causes.
Southport MP Patrick Hurley said his thoughts were with the families of Alice, Elsie, Bebe and everyone whose lives were changed by the attack.
He said: “The passing of time does not lessen grief or erase trauma. But it has also shown the strength, compassion and determination of our town.
“Through the kindness people have shown one another and through the charities and community organisations created in the aftermath, we have seen a lasting commitment to supporting others and ensuring that hope can grow alongside remembrance.”
He added: “Today we simply pause to remember, to reflect and to hold all those affected in our thoughts.”