Nice start. You described the marshmallow study as experimental. Were participants randomly assigned to different conditions? How were the attentional conditions manipulated and how were the rewards were presented in each condition?

The description of the age range is a bit confusing (3 to 5 years and 8 months; middle age of 4 years and 6 months).  What is the range of ages, and how were children recruited? 

I look forward to your update!