It depends upon the reason for the period pain, I know from childhood experience of years and years of period pain.
If a hot water bottle and ibuprofen/paracetamol mix doesn't touch it, it may need some investigation by doctors.
Buscopan is useful for some as it helps the digestive system and bladder relax BUT it's only useful if tenseness is the cause of the pain.
My own problems stemmed from an imbalance of prostaglandins compared with other hormones....prostaglandins cause the uterus to contract - levels are very high during labour, for obvious reasons, but can also happen during a period. In my case it was so bad I had a 'mini labour' type experience every time my uterus shed period blood.
Ibuprofen can help but maybe not strong enough. Some studies have shown good Vitamin D levels help break down the prostaglandins, as does an anti inflammatory diet.
If nothing helps, the doctor may prescribe prostaglandin inhibitors, such as mefenamic acid (ponstan forte). These were very hefty tablets but were the only thing which worked for me. They may not be prescribed for a young child however, it depends on age.
Don't be fobbed off by doctors as I was for years...I once had a woman doctor tell me "we all have to suffer period pains, we're women". It was shocking. I was missing school every month and later on, a couple days at work every month. It was actually a male doctor who took me seriously and did some tests, the tablets I took gave me a normal life back.
After I had my children, I opted for a hysterectomy as the periods were still very bad even though I was much older. Best operation I ever had.....