Parents at bedside of badly burnt boy

A 10-month-old boy allegedly burnt after being left in a scalding shower while his mother's boyfriend smoked a cigarette has spent the night in hospital.

The boy is in a critical but stable condition, placed in an induced coma at Westmead Children's Hospital with serious burns to 40% of his body, significant head injuries and severe bruising to his skull, face and jaw.

His distraught mother was on Monday at his bedside and his biological father had flown in from Queensland to be with him.

The 23-year-old accused of leaving the boy in the shower has spent the night behind bars after being denied bail at Penrith Local Court on Monday.

He is due to reappear in court via videolink on December 14.