Behind for sure and a lot of the things you mention would put him on the autism spectrum - the aversions, the delays in speech and understanding, the limited ability to use imagination, limited play skills, apparent lack of peer awareness - what others are doing (following others to kitchen), inability to copy ( what others do with the playdough).

So much of learning is tied to language but a more important measure is the social development because we take our cues from others, we copy others, we need to be on the same page as others when growing up and interacting and school is based on a group mentality.

Using one of the assessments such as that Nippising development scale and then sharing it with the parents - or even give them a copy and you keep one and both of you do your own assessments as the child may be producing different things at home because they are comfortable in the environment and interacting one on one with an adult. At the same time when you show them what child is like at daycare and ask them to take it with them to a doctor's appointment or their first words appointment so the person can get a reading of where child's needs are it should also alert a professional that they are dealing with something more than slow to develop oral speech.

I would be less concerned if the child's understanding was better even though their actual verbal was delayed. For sure it sounds like some form of cognitive learning disability with or without an actual syndrome diagnoses. Melissa has learning disabilities - cause unknown and was in special classes most of the way through school. Her language was delayed and she did fine developmentally for the first 18 months and then she started to progress slower and slower to the point she was a whole year behind when she started school and then fell further and further back all the way through.