Being you're from Lincoln Park, yes the Passaic is right there, but with a 4-year old, I'd tried to find a place with a little easier access. There is TONS of poison ivy almost everywhere along the river (not fun!).
To be almost guaranteed some fish, with tons of easy access, I'd try Verona Park lake in Verona off of Bloomfield Ave. Its a beautiful park with the lake itself being a little bigger than your typical park pond. I've caught some very respectable Largemouths in there (up to 19"), as well as Sunnys, the occasional Trout, and there are monster carp in there. If the little guy's attention span is short that day, theres always the playground for her
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