Walt Disney Co is also ending sales of toy guns at its parks, banning visitors over the age of 14 from wearing costumes and adding randomized secondary screenings of visitors with metal detectors.
Guests at Disney theme parks in Anaheim, California, and Orlando, Florida, previously had their bags checked by hand and with a handheld metal detector, officials said.
The moves follow a Dec. 2 shooting rampage that killed 14 people in San Bernardino, California, by a married couple inspired by Islamic State and Nov. 13 attacks in Paris in which 130 people died.
The theme park companies did not refer to either event in announcing the increased security, although Disney did say it was increasing security in light of recent events. Anaheim is about 50 miles (80 km) southwest of San Bernardino.
SeaWorld Entertainment Inc is also using metal detectors at its Orlando park, according to local media reports.
Universal is testing the use of metal detectors at its Orlando and Hollywood, California, parks but not in response to a specific incident, spokesman Tom Schroder said.
"We just want our guests to feel safe," Schroder said. Universal Studios Inc is owned by Comcast.
At Disney's Florida parks, more uniformed law enforcement officers will be patrolling the parks, and less visible security measures are being enhanced, the company said.
"We continually review our comprehensive approach to security and are implementing additional security measures, as appropriate," Disney said in a statement.
A man was arrested last weekend after trying to bring a gun into Disney's Magic Kingdom park, the Orlando Sentinel newspaper reported. The Magic Kingdom is one of four theme parks at Walt Disney World.
SeaWorld said that metal detection wands would be used to screen park guests.
On Thursday, school districts in Miami and Fort Lauderdale, Florida, were among several around the United States to be threatened with violence. The districts increased security in schools as a precaution, but officials said they did not consider the threats credible.
(Disclosure: Comcast is parent of Universal Studios and CNBC.)