What appeared was a flood of cheap, simple products on shopping platforms. She picked a string puzzle — a small board with holes and tangled cords — priced at less than 20 yuan ($2.93). The goal is to untie the knots and free the strings by moving them through the right holes.

"At first, my mother thought it would be too hard. So I showed her," Chu said. "Then she tried herself and realized that as long as she is patient, she can always solve it."

Within days, her mother was demanding more challenge.

"She told me to tie it tighter, twist it a few more rounds, and make it harder for her," Chu said.

The toy's appeal lay in its simplicity. Her mother soon started playing for hours. Then she asked Chu to buy the same toy for her elder sister.

"My aunt loved it too. And then she started playing with her own family, setting puzzles for each other. It brought the whole household together. Activities like watching TV are just input with no interaction. But with this toy, her brain is working," Chu said.

Yet, while such toys help some, others face more complex needs that off-the-shelf products fail to meet.