Jerry P is absolutely correct as a more than 4" wide opening may allow a child's body through but not their head. Kid hangs there and strangles. There's a dam good reason for that code.
Now, can anybody tell me why the spacing at the stair balusters allows a 4-3/8 inch opening? There are two basic stories and I've already chosen the one that makes the most sense to my alleged mind.

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Jerry McCarthy
Construction Consultant
www.expertbuildingconsultants.com