About 70 protesters have brightened the day of asylum seeker kids locked up in a Brisbane detention centre by hitting tennis balls to them over the fences.

“We love you, we love you all,” the asylum seekers call out from behind the chain-link fence.

Men, women and children gather on the grass in front of the steel bungalows to watch the activity outside.

About 70 protesters are chanting “free the refugees” and “freedom, azadi [liberty]” along the perimeter fence of the Brisbane Immigration Transit Centre at Pinkenba on a torrid, windless afternoon.

Every few minutes passenger jets approaching the nearby Brisbane Airport drown out their chants.

But the protesters, including children, youths, middle aged and elderly, continue to call out.

Some use racquets to hit tennis balls over the fences to the asylum seeker children, who squeal and laugh in excitement.

A plain-clothes guard casually wanders through the grassy no-man’s land between the perimeter and inner fences collecting stray balls and handing them to the detainees.

A small group of police watch the demonstration for about five minutes.

“I’ve seen what I need to see and I’m comfortable with this situation, so now we’re going back to the station,” an unnamed police sergeant tells AAP, before driving off.

Veteran refugee advocate Margarett McPherson claims someone told police the tennis balls contained explosives.

“How outrageous,” she tells reporters.

The long-time Refugee Action Collective member said finding out about the Cambodia resettlement plan and reintroduction of Temporary Protection Visas on Friday was a double blow for human rights advocates.

Even without those deals in place, Ms McPherson said it was appalling that children were being “locked up” by the federal government.

“I’ve got little grandchildren from one (year-olds) upwards, and I just can’t believe that we do this to children,” she said.

“Children should be free, not to mention their parents, but children, I mean it just appals me.

“Refugees have so much to offer, they want to be Australians, they want to be part of the community.”

In the background the asylum seekers bounced their new tennis balls and waved at the protesters: “we love you, we love you, Australians.”