<p>In this research, the carbon quantum dots (CQDs) with a particle size of 8.0 nm, quantum yield (17.8) and long period of stability 60 days were prepared under a simple, eco-friendly, low-toxic and low-cost one-step hydrothermal method by employing biomass rheum ribes (R. ribes) as precursors for detection purpose. The widely recognized heavy metal element is lead (Pb²⁺), and the pollution it causes has received considerable attention. Therefore, it is both essential and extremely difficult to develop uncomplicated and efficient techniques for the detection of lead ions (Pb²⁺) in kids' toy samples. The study focused on the detection of lead ions (Pb²⁺) in kids’ toy samples. The presence of heavy metals in toys poses significant health risks such as cancer, kidney disorder, behavioural disorders, increased aggression bone and brain tissues, due to their potential toxicity and bioaccumulation. Lead is a global priority pollutant. The investigated results were processed by a fluorescence spectrophotometer under optimum conditions with excitation and emission wavelengths of 330nm and 406nm, respectively. Fluorescence of CQDs was quenched efficiently and sensitively by lead (Pb²⁺) ions, throughout some other common metal ions. The linear range is wide (0.01–21.0μg/mL) with the detection limit (0.00974μg/mL), limit of quantification (0.0325μg/mL), and (R² = 0.9939). The recovery of Pb²⁺ ions, which cause quenching of fluorescence intensity, was mostly more than 90% (n = 3). The results show high contents of Pb²⁺ in kids’ toy samples. The concentration of Pb²⁺ in the samples under study was over 100μg/mL after multiplying the corresponding dilution factors. The intense quenching effect of carbon dots can be attributed to the efficient binding of lead ions on their surface. Later, it was proposed and established that aggregation-induced quenching is the working principle of carbon dots' interaction with Pb²⁺ ions.</p>