The zoo sits on the west side of the river and goes uphill, which is the thing to plan around. John Ball, a lawyer who had crossed the continent overland in the 1830s, left the city forty acres; a zoo opened on them in 1891 and has since spread across roughly a hundred and forty, holding more than two thousand animals.
Arrive early. The car park fills on a warm Saturday, and the first hour is the coolest and quietest part of a summer day for both you and the animals.
Work uphill first, while everyone still has legs, and come down through the flatter sections at the end. The Bill Idema funicular carries you to the treehouse at the top and is worth doing at least one way — for a four-year-old it is frequently the highlight of the whole visit, which is a useful thing to have in reserve.
Budget three to four hours. It is not an all-day site, but it is more physical than a flat zoo of comparable size, and families consistently underestimate that.
Bring water and a layer. The hillside is shaded in parts and exposed in others, and West Michigan afternoons swing more than the forecast suggests.
Afterwards, John Ball Park at the bottom gives you somewhere to let everyone run out the last of the energy before the drive back, and the West Side restaurants on Bridge Street are five minutes away.