Women in blue cloth hairnets sew the finishing touches on plush pink piggies and orange stuffed foxes, before tossing them onto giant piles in Maria Liao’s factory in southern China. They will be boxed and shipped to the United States, where many of Ms. Liao’s clients are based.

The factory is quieter than it should be. Orders are down this year, as Ms. Liao’s customers hesitate in the face of a succession of tariffs that President Trump has put on products coming from China, another round of which will probably come this week. The duties have upended small businesses in the United States that depend on factories in China to build the things they design and sell.

The tariffs are also reverberating on the other side of the ocean in two-floor factories like Ms. Liao’s Dongguan Yarunli Toys.

“We are helpless,” said Ms. Liao, 33, who runs the factory with her older brother. “I don’t know what the next quarter will be like.”

Ms. Liao is one of millions of people in China who sew, cut, build and assemble the toys, clothes, tools and cars that Americans use every day. The work they do allows companies to make and sell things to households in the United States quickly and cheaply.