The 18-month-old little boy and girl are being farewelled at the Hemmant Crematorium and Chapel, on the city's southside, where a lengthy service was earlier held for about 50 people.

After the ceremony, a pair of tiny white coffins were brought from the chapel for a second open-air ceremony, where about three dozen brightly-coloured balloons were released by mourners.

The pair will be buried later this morning.

The childrens's father, who is charged with murdering and torturing the pair, was earlier this week barred from attending the service by a Supreme Court judge as a condition of his release on bail.

Their mother, who is facing the same charges, is in custody on remand.

The toddlers were found dead in their cots in the family's Sunnybank Hills home on June 16, weighing little more than newborn babies.

Police allege they had starved, and had lain dead in their beds for more than a week before they were discovered.

The married couple, aged 30 and 28, have also been charged with failing to provide the necessities of life.