Research by Consensus Action on Health (CASH) found that, out of 189 child hospital meals, 85 of them would be considered too unhealthy were they served in a school environment under guidelines introduced in 2008.
A chicken tikka masala and rice dish served in hospital was found by CASH to contained 14 times as much salt (2.2g) and 8.5 times more saturated fat (6g) than a chicken and vegetable balti served in a school.
Professor Graham McGregor of the Wolfson Institute of Preventive Medicine and chairman of CASH, said: "With everything we know about the risk of children developing high blood pressure and diet-related diseases, such as obesity, it is vital to keep their consumption of salt and saturated fat as low as possible, while still being appetising."
"When such great progress has been made on what pupils are eating in school, it is shocking that children in hospitals are being ignored."
According to MP Joan Walley: "It is really important that children in hospital are served food which they like, but we must also make sure that it is nourishing and healthy for them to eat."
A Department of Health spokesperson said: "We recognise the importance of good-quality food for patients of all ages, both in terms of improving their health and in relation to their overall experience of services.
"Tools are available to support caterers in assessing the nutritional content of meals."