M0nica
Actually, at this age, I wouldn't call those skills essential. This child is only 3 years old. She is only just reaching a point at which she is starting to understand that people other than her have feelings.
Keep in mind, too, that requiring children to play only with children of their own age is actually a very artificial distinction. First of all, in a family, unless you are one of a set of multiples, there is no other child your own age. Not to mention that in the workforce we don't usually require people of similar ages to work together. She's being socialized by being around her parents and other adults. In fact, the evidence is demonstrating that quality serve and return interactions with a responsive caregiver is the single most important factor in brain development for children.