Richard Coleman, 29, got rid of his frustrations by fracturing a seven-week-old girl's skull and breaking the arm of a baby boy, it was alleged.
Mr Coleman, a specialist nurse in the cardiorespiratory ward at the hospital in London, dismissed the injuries suffered by the babies as unfortunate accidents.
But Louise Kimill, prosecuting, said the girl's smashed skull could have been caused by swinging her by the legs and banging her head against an object. And the seven-month- old boy may have had his arm broken by being picked up roughly from his cot.
Ms Kimill told Snaresbrook Crown Court: 'It is particularly stressful work in the cardiorespiratory ward working with sick children who often have breathing problems.
'On the morning of the incident with the little boy the defendant made an entry in the accident register saying he had slipped on a toy while holding the baby and caught his left arm. But he claimed the baby moved his arm freely and had settled down to sleep. In fact he had broken the baby's arm.
'He says it was a ghastly accident but the prosecution say this is nonsense.
It is nothing of the sort, it was a deliberate act.'
The jury was told that an investigation was carried out and hospital managers accepted his explanation, and he continued to work at the hospital.
But six months later, the baby girl suffered a cracked skull and a fractured ankle while in Mr Coleman's care, Ms Kimill said.
She added: 'The defendant said he had no idea how the injuries had occurred.
But he explained a bruise on her thigh had been caused when he had wrapped her too vigorously.
'The defendant said on the night of the incident he may have been rough. He said he was tired and may have been abrupt with her when picking her up. He said may have been rough and not careful enough.'
Mr Coleman, a father of two children who is separated from his wife, and who lives in a Christian hostel in Ilford, Essex, denies charges of causing grievous bodily harm with intent and of causing actual bodily harm on 28 February and 21 September last year. The case continues.