We examined the effects of singular versus dual task constraints involving upper and lower extremities in typically developing children in young (4-6 years old), middle (7-9 years old), and old (10-13 years old) age groups. The purposes of this study were: 1) to investigate the effects of singular upper and lower extremity and dual upper and lower extremity conditions on motor variability and 2) to examine if variability in children's motor actions would differ according to age (i.e., young, middle, or old). Twenty-four children (M age=8.7; SD=3.7) completed three tasks: finger rotation (upper extremity singular task constraint), obstacle crossing (lower extremity singular task constraint), and box carrying while walking (upper and lower extremity dual task constraint). Compared to the old age group, the young age group displayed more variable rotation strategies during clockwise (χ2(8, N=24)=12.4, p=0.046) and counterclockwise finger rotation (χ2(8, N=24)=12.8, p=0.047). During box carrying, children in the young age group had the most motor variability in their stride length, velocity, the vertical positioning of the box, and minimum and maximum joint excursion (all ps<0.05). Crossing leg frontal plane hip angles were more variable on low versus high obstacles (all ps<0.05). Our results suggest that four- to six-year-old children may still be developing the ability to produce consistent motor actions, especially under dual-task constraints. Examining children in the context of completing tasks with a variety of constraints may be useful in assessing the development of children's motor variability.