Sorry because this is a little hard to see, but my favorite I've seen so far is the below. You could also do either tension wire or metal.

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My dsl used clear plexiglass panels on his stairs when grands were little. He cut the panels to fit, drilled holes on each corner and attached to rail with links from a chain. You could see through but kept little bodies safe

Are the openings on your current bars too big for current code? Is that the problem for kids? Otherwise I would just paint them black. Also, I would avoid anything horizontal since kids tend to be little monkeys climbing on everything and horizontal is just asking for trouble.