You should never use a weighted blanket on infants and small children (age 4 and under) as it increases suffocation risks. Weighted blankets are not safe at this age. 

Weighted blankets designed for older children are smaller in weight and size compared with the blankets for adults. Weighted blankets should only be 10% of a person's total weight. This means most adult weighted blankets aren't suitable for older children; they will be too heavy. Choose one specifically designed for children to ensure that it's correctly proportioned. 

Here are the key things to consider when letting older children use weighted blankets: