At this point your kid is smarter and more intelligent as compared to his infant stage. He has started his school and is learning about new lessons. However, this is also the time when kids might develop fear about different things.
Most children have the fear of fire, water or height. Do not let this fear transform into any type of phobia. You as a mother need to make your child psychologically strong. You have to cut this fear through different activities.
What you can do
If the kid is afraid of water then you can take him for swimming lessons. Make sure the water level is not too much. Be there with the kid and encourage him to enter the water. You can use floaters in the beginning so that the child feels safe. Hold him and make him flap his hands and legs in the water. Once he gets comfortable then you can ask him to cover a certain length on his own. The fear of fire can be erased by asking the child to light a candle. Do not let him become weak and be there to motivate him.