Giving Leads to Happiness in Children Figure 1. Happiness displayed in each preliminary study and main experiment condition. Happiness, as rated by coders, for children in the preliminary study and five phases of the main experiment. Error bars represent 95 percent confidence intervals around the mean. doi:10.1371/journal.pone.0039211.g001 compare giving and other positive social interactions, they provide suggestive evidence for the emotional benefits of giving in toddlerhood, and the impetus for a controlled experiment in which emotional expressions to giving and non-giving could be examined within individual toddlers. In our main experiment, each toddler received treats and gave them away, under conditions in which giving was or was not personally costly. The experiment began with a warm-up phase designed to acclimate toddlers to the experimental situation. Each child was introduced to several puppets who ‘‘liked treats’’ and watched the experimenter give each one a treat (either Goldfish crackers or Teddy Grahams; one kind of treat was used in the warm-up and the other in the main study, with treat type counterbalanced). Puppets ‘‘ate’’ the treats placed in their bowls, by making ‘‘YUMMM’’ eating noises and pushing them through the bowls’ false bottoms. In addition, children gave treats to the puppets and received treats themselves (additional details in methods summary). We assumed that children would believe that the puppets ate and enjoyed the treats because previous research has shown that infants and toddlers attribute perceptual states, goals and desires to non-human agents [25,27–30] (cf [31]). Indeed, research suggests that toddlers can distinguish between individual puppets’ preferences for different kinds of treats [32]. After the warm-up, participants moved to the testing phase. Children were (a) introduced to a new puppet (‘‘Monkey’’), encouraged to touch it, and told it liked treats. The experimenter said ‘‘Both you and Monkey have no treats right now,’’ to draw children’s attention to the limited nature of this resource. The experimenter then (b) ‘‘found’’ eight treats, said they were all for the child, and placed them all in the child’s bowl. Next, the experimenter (c) ‘‘found’’ a treat and gave it to the puppet, (d) ‘‘found’’ another treat and asked the child to give it to the puppet, and (e) asked the child to give the puppet a treat from the child’s own bowl (see Figure 2). Participants’ happiness during each phase was coded by the same research assistants using the same scale as in the preliminary study (average alpha = .84). Phases (c) – (e) were counterbalanced; there were no significant order effects on children’s happiness (ANOVAs, ps ..095). Results A repeated-measures ANOVA indicated that children’s happi- ness levels differed across the five study phases (F(4,72) = 6.76, p,.001). Testing our key questions, we found that toddlers did not find giving aversive; rather, they exhibited greater happiness when giving treats to the puppet than when receiving treats themselves. This held true both in phase (d) when toddlers gave the puppet the treat that the experimenter ‘‘found’’ (repeated measures ANOVA F(1,18) = 5.58, p,.04, d = 0.88), and in phase (e) when they gave the puppet their own treat (repeated measures ANOVA F(1,18) = 15.84, p,.005, d = 1.35; Figure 1; sample video clip can be found online at http://cic.psych.ubc.ca/Example_Stimuli.html). Critically, a comparison of phases (d) and (e) revealed that toddlers were happier when giving away their own treat than when giving the ‘‘found’’ treat (repeated measures ANOVA, F(1,18) = 4.52, p,.05, d = 0.46). This difference emerged despite the fact that in phases (d) and (e) the child’s interaction with the puppet (i.e., taking a treat from a bowl and placing it in the puppet’s bowl) was exactly the same; the sole distinction between these phases was the source of the treat, with the child sacrificing his/her own treat only in phase (e). This comparison acknowledges the personal sacrifice often involved in prosocial behaviour, and suggests that rather than finding such acts aversive, children find them emotionally rewarding. To test the possibility that children’s positive responses to giving were driven by the puppet’s reaction to receiving treats, our coders also rated how much enthusiasm the puppet displayed in each phase. Puppet’s enthusiasm was uncorrelated with children’s happiness in any phase (Pearson’s correlation coefficient rs from .00 to 2.21, ps ..25), suggesting children’s happiness was not a function of puppet enthusiasm. PLoS ONE | www.plosone.org 2 June 2012 | Volume 7 | Issue 6 | e39211