I agree with Arthur. I would not entertain putting such a young child into a competitive situation. Nurture the ability by all means but don't put him into a situation where he's likely to encounter a lot of completive and highly protective parents. Children under 6 are emotionally very underdeveloped and their cognitive function is still quite restricted.
Play football with him in the garden/park and give him lots of gentle encouragement, but remember he's playing, not competing.
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