Lisa Williams, 31, left the love message along with five bars of chocolate for each of her children before setting off to the beach.
Less than an hour before she died in the visitors' shelter, Mrs Williams posted a picture of the St Valentine's card with the loving message next to the chocolate bars.
She wrote: "I love you with all my Welsh heart … will see you all I promise."
Lisa Williams left a card and chocolates for her children
She detailed which chocolate bar was for which child
Her children, aged five to 14, were being cared for by relatives after the tragedy. She specified which chocolate bar was for each of her children in the message and also left a necklace to one of her daughters.
In it she wrote: "Chocolate treats for you all off mam."
She then spelled out all her children's names and giving each a Galaxy Smooth, Galaxy Smooth Caramel, Malteasers or Milkie Bar.
She then wrote: "Kind hands, kind feet, nice words and caring is sharing."
Her children are aged five to 14
To her eldest daughter she wrote: "The necklace is for you. You're old enough to wear it. Love Mam xxxxxx".
A security guard found the body of Mrs Williams in a public shelter close to Newry beach in Anglesey on Sunday night. Police are not treating the death as suspicious.
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Just hours before she went missing, Mrs Williams posted a message on Facebook saying: "Everyone makes mistakes in life, but that doesn't mean they have to pay for them the rest of their life. "Sometimes good people make bad choices, it doesn't mean they are bad. It means they are human."
One of her children children replied on Facebook writing simply: "Love u mam and miss u."
A security guard found the body of Mrs Williams
It is understood Mrs Williams had medical treatment and recently underwent a major operation (a hysterectomy for non-cancerous growth around the womb). Neighbours said had also recently parted from her boyfriend of nine years. It is also understood social services had been involved with the family. She was believed to be living in bed and breakfast.
One former neighbour said: "She's been through hell and back for different reasons recently. Those poor kids."
Dozens of messages from heartbroken family and friends were left on the Facebook page after news of her death broke – and offering their condolences to her children.
One wrote: "Your mam loved you and your brother's and sister so much. Im sure u all know that (sic)."
Mrs Williams had medical treatment and recently underwent a major operation
"Your mam was also so proud of u five. My heart goes out 2 u little one's (sic)."
Another said: "Your mam adored the bones off yous all, such kind and caring woman, she'll always be with you no matter what (sic)."
Mrs Williams' remains were found by a security guard from Holyhead port.
District Inspector Jason Higgins, at Llangefni Police Station, said: "The lady, who we believe to be local was pronounced dead at the scene.
Our thoughts are with them at this very difficult time."
Wyn Parry, Holyhead Port Operations Manager, said: "She was found by one of our security details. We are very sad to hear about it, and send our condolences to her family."
In the UK, the Samaritans can be contacted on 116 123.
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