playing alone, with no interaction with other children
playing cooperatively in a single-sex group
playing parallel to other children, but not playing together
playing and interacting cooperatively in a mixed-sex group
Number 3 is correct.
Toddlers aged 2 1/2 – 3 years old typically engage in parallel play : They will play alongside others, but not necessarily play together. Playing alone with no interaction with others is seen in children under age 2. Playing in single-sex groups is typical of children aged 4 – 6, while playing in a mixed group of boys and girls is common with children aged 3 – 4.