My great-grandfather Robert Armstrong was born on a plantation in Clover, S.C., around 1850, and held in captivity until slavery ended in 1865.

Slave owner Jesse Armstrong valued Robert, who was a child at the time, at $800, according to his last will and testament. I treasure a black-and-white photo of Robert and every shred of what I can remember of my late father’s recollections, shared on Sundays at the dining room table. They are links to my family’s not-so-distant past — a past that I try not to dwell on for obvious reasons.

But Sunday marks the 400-year anniversary of the first documented arrival of Africans to an English colony in what is now the United States. Their subsequent enslavement would come to be known as America’s original sin, and the nasty stain it left on this city and nation lingers to this day.

I’m reminded of it every time I drive through impoverished neighborhoods in Philly and see residents mired in generational poverty. I’m reminded of it every time I read another story about substandard inner-city schools. I’m reminded of it every time some conservative tries to downplay the horrors of the institution or objects to hearing about it, like those idiotic tourists did recently after a tour of Louisiana’s Whitney Plantation.

We need to always remember how the seeds of white supremacy were planted 400 years ago Sunday.

So here’s my proposal.

Instead of heading to the Jersey Shore to enjoy one of the last beach days of the summer, help your children understand the significance of what happened in 1619.

Some have said that focusing on 1619 is misguided, since it ignores the presence of Africans in South America, the West Indies, and elsewhere at that time. I’m not going to quibble about when slavery actually started. I’ll leave that to the historians. Frankly, I’m happy that any attention is being paid to the subject, given how poorly it is taught in most schools.

“We’re still living with the remnants of this system, and children will probably notice, for instance, that certain neighborhoods are mostly black and other neighborhoods are mostly white, and they may want to know why," said Maureen Costello, director of Teaching Tolerance, a project of the anti-hate Southern Poverty Law Center. “That requires a little bit of history. Parents should be ready to talk about the things that are obvious."

One way to begin the conversation is to take your children to an event on Sunday at the President’s House at Sixth and Market Streets, on Independence Mall.

Avenging the Ancestors Coalition, a Philadelphia-based advocacy group, is planning a major commemoration of the 400th anniversary of the arrival of Africans to America. Organizers plan to have 400 children carry signs, each with a number representing a year from 1619 to 2019 during an event scheduled to start at 2:30 p.m. (To participate, children between the ages of 4 to 14 are asked to arrive in white T-shirts at 1:30. Volunteers will be selected on a first-come, first-served basis.)

“Black children must constantly be reminded of slavery from the past, because it explains our pitiful economic, educational, social and political condition in the present," explained lawyer Michael Coard, the event’s organizer. “Slavery, along with its direct and legal offspring, meaning the Redemption Era, sharecropping, convict leasing, peonage labor, Jim Crow, voter disenfranchisement, gerrymandering, redlining and the like — still adversely and constantly affect black people to this very day.”

As for me, I hope to devote part of Sunday to reading last week’s New York Times Magazine, which is dedicated to coverage of the 1619 anniversary. I’ll lie on the beach, reflect, and wonder what old Robert Armstrong and the other ancestors would make of all of this.