It is not uncommon for children to break their arm, especially when they play sports.
However, while the doctor will no doubt give you plenty of advice on what to do to ensure the break or fracture heals properly, there are a number of things you can do to help:
Don’t let them participate in sports
It is important you don’t let your youngster participate in sports or any other contact activities that may cause them to fall or injure themselves further until they have thei doctor's approval.
Keep it dry
When they get a waterproof cast they should be able to go about their daily cleaning tasks as normal but until then you will need to cover it up when they are bathing. Stick to the bath for now – it will be easier to keep the cast dry. However, even when they do get a waterpoof cast you will still need to give them a helping hand, as they may struggle to wash themselves. You don’t want the cast to get wet on the inside as it may cause the skin to become sore and irritated.
Keep the cast clean
It is important you keep your child’s cast as clean as possible. The area under the cast is likely to get all sweaty and may begin to smell slightly, especially if it has been on your child’s arm for a couple of weeks or more. Ensure they shower and keep the outside of the cast clean.
Wash the area under the cast 
Once the cast has been removed you might notice a little residue along the area that was covered by the cast. This is simply a build up of dead skin and sweat -so there is no need to worry about it. Just give it a gentle wash and it will be back to normal.  
Don’t use a needle to scratch underneath the cast
Make sure your youngster doesn’t use a knitting needle to scratch under the cast as this can poke into the skin and cut it. Instead blow down the cast with your breath or gently blow cold air from the hairdryer.
Be patient with them
Your son or duaghter may be reluctant to move or use their arm once the cast is taken off. Obviously the accident is still going to be fairly fresh in their mind and they might be worried about it happening again. Try to be patient with them and encourage them to start using it again slowly.
Do what their doctor says
Above all else, make sure you follow the doctor's instructions.