Most itineraries treat Iguazú as a half-day stop between Buenos Aires and Rio: fly in, walk the boardwalks, take the photo, fly out. We did that math and it didn't add up — not for what the falls actually are, and not for traveling with a kid who wanted to actually look at things instead of being marched past them.
Argentina side vs. Brazil side
The Argentine side gets you close — walkways that put you right above and beside the water, including the Devil's Throat circuit, which is the main event and deserves unhurried time. The Brazilian side gives you the postcard view: the wide, panoramic shot of the whole falls system from across the gorge. They're not redundant. Skipping either one means missing half the story.
What it actually costs
Park entry on the Argentine side and the Brazilian side are separate admissions, and if you're staying near the border you'll likely cross between the two countries — factor in whether you need a visa for Brazil ahead of time, since that's the detail that catches people off guard. Budget for two full park days rather than one rushed one; the marginal cost of the second day is small compared to what you get out of it.
Pacing it with a kid
The boardwalks are long, hot, and genuinely thrilling for a while before they become just long and hot. We split each day into a morning session at the falls and an afternoon doing something completely different — the boat ride under the falls, if your child is up for getting soaked, is the single best "we're not just walking anymore" reset we found.
The one thing we'd do differently
We'd book the boat ride for the first day, not the second — it's the highest-energy activity and works better as an opener than a finale, when everyone's already tired.