It's the cost that counts! Young children's reciprocity is sensitive to subjective cost.

Three experiments investigated whether reciprocity in children aged 4-7 (N = 192; 53.12% female; 65.63% White) is sensitive to the cost of a gift from the benefactor's perspective. In the main study, 6- and 7-year-olds, but not 4- and 5-year-olds, preferred to reward a benefactor who valued a gift highly over one who gave an identical gift but valued it less. A follow up study found that 5- but not 4-year-olds at least expected object valuation to impact sharing. In the third study, 6- and 7-year-olds even rewarded a benefactor whose gift they themselves (the children) valued less (than another's gift) if that benefactor herself had valued it highly. Increasingly over age, young children's sharing and reciprocity consider subjective costs.