Yes, he needs a separate passport for sure. Not sure about the visa; best thing you can do is call up and find out.
But from the belgian usa website:
My children are included in my passport. Do they need their own passports to go to the US under the Visa Waiver Program?
Children, even infants, need their own machine-readable passports for travel under the Visa Waiver Program.
and if you wonder what does infant mean:
The term infant is typically applied to human children between the ages of 1 month and 12 months; however, definitions vary between birth and 3 years of age. A newborn is an infant who is only hours, days, or up to a few weeks old.
You can go to your own country's usa website and also see what it says about the visa...
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