Former senior police officer Marius van der Westhuizen, who allegedly killed his three children, wept in the Cape High Court on Monday as he spoke of his love for them.

"I was never aggressive towards them. I only gave them love," said Van der Westhuizen about his relationship with his children as he took the stand in his own defence.

He said his marriage to Charlotte, the mother of two of the three children, was happy, and they both were "full of excitement" as they awaited the birth of their first son, Marius, nicknamed "Boetietjie".

"Boetietjie's birth was a gift from above, and the best thing that ever happened to me," said Van der Westhuizen.

He is on trial before Judge Willem Louw and assessor M Powell, on three counts of murder, after allegedly shooting dead Marius, who was eight at the time, his daughter Antoinette, 21 months, and a handicapped daughter Bianca (16) on 28 July 2006.

On Monday, during his testimony, Van der Westhuizen recalled buying Boetietjie a toy lawnmower and weed eater for his first birthday and tearfully told the court of the way the toddler would grab his toy lawnmower and join his father mowing the lawn.

As the boy grew older, Van der Westhuizen said they did everything together.

He recalled how his son, seated next to him in the family vehicle on their way to a holiday, asked if he could join his father to go fishing.

Defence attorney Milton de la Harpe asked Van der Westhuizen about his relationship with mentally handicapped Bianca.

Van der Westhuizen wept as he told how special and so full of love she had been.

He said he was very protective towards her, perhaps over-protective, because he feared she would hurt herself.

Because she was handicapped, he said she did not understand the things girls of her age did.

One could only buy her a few things which she understood and loved like a colouring-in book and crayons.

Van der Westhuizen told of an occasion when she hit her best friend in the face with a belt.

He told the court: "I scolded her, I could not give her a hiding because she could not understand. She did not know right from wrong."

He said she was born by Caesarean section, because she was situated in the womb feet first.

Prior to her birth, she suffered a brain infection, which caused her "floppy neck syndrome", which left her speechless and semi-paralysed.

The case continues on Tuesday.