I presume that as a first step a colostomy has been done. This would mean that a loop of her large intestine has been brought out in the abdominal wall through which she passes stools. Children who have a colostomy are more prone to have diarrhoea since the large intestine is the site of water absorption. You must also realise that some stool spills over from one limb of the colostomy into the other end. And since the end of the large intestine is closed, this spilled over stool has no passage out. But it does give the baby a sensation of fullness and the baby strains to pass it. That is why the baby often goes red in the face at the time of straining. You may consult your paediatric surgeon and consider doing a wash out of the distal loop.