Diseases are not static and very few, if any, are episodic. I know of no disorder where a child will get pain once a week or so, that too always at night. I suggest a firm diagnosis should be made before drugs are given.
Nise (nimesulide) is not allowed to be used by even adults in advanced countries like United States, Great Britain, Canada, Australia etc. The question of using it in children simply does not arise.
In few European countries where it is allowed in adults, it can only be prescribed in four conditions: osteoarthritis, rheumatoid arthritis, ankylosing spondylitis and dysmenorrhoea (females). Its use even in older children (6-12 year) was banned early in 2003. It was never permitted in children below 6 years. In India, an 8-month old child in Kerala died in 2002 when nimesulide was given to him.
The only safe medicine for children both for fever and pain is paracetamol (such as Crocin, Calpol etc.). Alternatively one can use ibuprofen or in very severe cases a combination of ibuprofen and paracetamol (such as Combiflam suspension).