Two were injured when the suspected tornado touched down near the cities of Hearne and Franklin.
The Angelina County Sheriff's Office said an eight-year-old and a three-year-old died when strong winds toppled a tree onto the back of their family's auto in Lufkin while it was in motion.
The storms are part of a large system moving through the southern U.S. They were in the back seat with their parents in the front, said Angelina County Sheriff's Department Capt. Alton Lenderman.
National Weather Service meteorologist John Moore said a possible twister touched down Saturday in the Vicksburg, Mississippi, area.More news: Apple to Split iTunes Into Separate Apps
The Storm Prediction Center has issued a moderate risk (level 4 out of 5) for severe weather Saturday across parts of the Lower Mississippi Valley. No injuries have been reported, but officials said several businesses and vehicles were damaged.
Trees were pulled up by the roots, roofs were torn off buildings and the cinderblock foundation was all that was left of a mobile home in the town, which is southeast of Waco. Trees were down throughout the hilly city on a bluff overlooking the Mississippi. University spokesman Sid Salter said some debris, possibly carried by the tornado, was found on campus, but no injuries were reported and no buildings were damaged.
Emergency radio traffic indicated that search crews were having difficulty reaching damaged structures due to downed trees and power lines in the roadway.
The large storm system also knocked out power to thousands and caused some flash flooding. Franklin is located about 200 kilometres south of Dallas. Severe storms crossing a big swath of the South, including parts of Louisiana and MS, have knocked out power to thousands and caused some flash flooding.More news: #RewriteTheRules with the Huawei P30 series
The severe weather threat Sunday places almost 100 Million Americans at risk of risky storms, tornadoes, hail and severe wind gusts, CNN Meteorologist Derek Van Dam said.
A preliminary damage survey found that a tornado with peak intensity of EF-3 and winds up to 140 miles per hour touched down in Robertson County, according to the National Weather Service in Fort Worth.
Two people were taken to a hospital with injuries that aren't thought to be life-threatening, Yezak said. Some people had to be extricated from their homes. KTRK-TV also noted the storm had winds of 60 miles per hour in Cherokee County, which is near Angelina County, where the fatalities occurred. Alto is situated about 225 kilometres north of Houston.More news: Pogba 'believes' Manchester United can still 'hurt' Barcelona