The 21 line: what it covers
In Nevada you must be 21 to gamble, to drink alcohol, to buy cannabis, and to enter nearly every nightclub, dayclub, adults-only pool and topless revue. "Gamble" is broad: it includes placing a bet at a sportsbook, playing a slot machine, standing at a table while a companion plays and, at most casinos, standing still near gaming at all. There is no exception for 18-to-20-year-olds, no exception for a parent standing beside them and no exception for a foreign visitor whose home country allows drinking at 18. A casino that lets a 19-year-old pull a slot handle risks its licence, so enforcement is consistent and unsentimental: winnings are confiscated and the person is escorted out.
Everything else, hotel rooms, restaurants, shows, attractions, pools that are not adults-only, shopping and the Strip itself, is open to all ages with the rules described below.
What 18-to-20-year-olds can do
An 18-year-old can check into a hotel room at some resorts and not at others; most Strip properties require the registered guest to be 21, though several set it at 18 and a few Downtown and off-Strip hotels do too. Confirm before booking, because a 20-year-old arriving alone at a 21+ property will be turned away. They can attend most shows, including Cirque du Soleil productions, residencies at the arenas and comedy that is not marketed as adult; some comedy clubs and all adult revues are 21+. They can eat anywhere, ride the High Roller, see Sphere, do the Strat thrill rides, visit AREA15 (which has 21+ hours in the evening), use the resort's main pool and walk the Strip. Some "18+" events exist, notably certain concerts and festival days, but the dance-music clubs are 21+ without exception.
Walking through a casino with children
Every Strip hotel is entered through its casino, so children walk through gaming floors constantly; that is legal. The rule is that minors must be accompanied by an adult and must keep moving along the marked pathways. They may not stop, sit at a machine, lean on a table, watch a hand or wait beside a parent who is playing. Security will approach quickly, politely the first time. Strollers are fine. The practical advice is to learn the route from the hotel entrance to the elevators, use the designated non-gaming corridors where they exist (Venetian, Aria, Wynn and Bellagio all have them), and never leave a child in a hotel room or an arcade while you play; that is treated as a child-welfare matter, not a house rule. See Las Vegas with kids and best family hotels.
The curfew rules (and how they work in practice)
Clark County and the City of Las Vegas have curfew ordinances for minors under 18. As generally written, unaccompanied minors cannot be on the Strip corridor on Friday, Saturday and holiday evenings after roughly 9 pm, and elsewhere after roughly 10 pm on weeknights and midnight on weekends, with exceptions for those with a parent, going to or from work or an event, and similar. The ordinances change and the numbers above are a guide, not the law; check the county and city codes if it matters. In practice, enforcement focuses on unaccompanied teenagers on the Strip and Fremont Street at night, and a family walking together is not stopped. Fremont Street Experience additionally restricts minors from the mall on certain nights and during some events, and posts those restrictions at the entrances.
Pools, dayclubs and adults-only zones
Resort main pools welcome children, with the usual proof of being a hotel guest. Adults-only pools (Bellagio's Cypress, Caesars' Venus, Mandalay Bay's Moorea, the European pools at Wynn and Encore, and similar) are 21+, as are all dayclubs, whether or not alcohol is served at the moment you ask. Some family-friendly pools have separate over-21 sections or hours; Mandalay Bay Beach is the best-known family complex with a wave pool and lazy river. The family pools guide lists what is open to whom and when. Arcades and family entertainment centers such as the ones at Circus Circus, New York-New York and Excalibur are all-ages, and Circus Circus's Adventuredome is the one indoor amusement park on the Strip.
Shows, restaurants and nightlife with under-21s
Most theater shows are all-ages, with some setting a minimum of 5 or so for practical reasons and adult revues at 18 or 21. Check the show's own age line before buying; the family shows guide highlights the reliable picks. Restaurants inside casinos are open to all ages, including the steakhouses and celebrity-chef rooms; bars that serve mainly alcohol may refuse minors, and any bar on the gaming floor cannot seat them. Lounges with live music vary. A parent taking a 19-year-old to a nightclub is a no; the same 19-year-old can, however, go to Sphere, a residency at Dolby Live or a concert at T-Mobile Arena. Sportsbooks are 21+ to enter at nearly all casinos, even to watch.
ID: what is checked and what is accepted
Expect to be carded for alcohol, casino entry after a certain hour, clubs, dayclubs and pool entrance gates. Accepted: an unexpired government-issued photo ID (driver's licence, state ID card, passport, passport card, military ID). Not accepted: a photo of an ID, a student card, a foreign ID without a passport at many venues, and anything expired. Anyone under 21 caught with a fake ID faces a citation, and the ID is confiscated. Parents can drink at dinner with a child at the table, but a child cannot be served, and staff are trained to refuse the "just a sip" request. For international families, the international visitors guide explains why a passport, not a licence, is the document to carry.
A realistic plan for a family day
Morning at the pool before the heat; late morning at an attraction that is genuinely for kids, such as Shark Reef, the Adventuredome, the Fremont Street canopy in daylight or an out-of-town trip to Red Rock; an early dinner at a resort restaurant; a family show at 7 pm; and back to the room by the time the Strip switches into its nighttime mode, around 10 pm, when the crowds, the noise and the card-slappers make the sidewalks less pleasant for children. Stay at a resort whose non-gaming route to the elevators is short, and see the family itinerary for a full plan.