I've had a 4 year old very similar to what you are describing. It turns out he has FAS and is massively delayed. His grandmother was main caregiver and didn't know, but we always talked about his issues similar to what you are talking about and now he is in the school system he has been flagged and is getting help. I would recommend for this little guy that you observe and document. Yes it is extra work for you, but it shouldn't take that much time per day to write a blurb in a book. Not your opinion, just your observations. I would also recommend you google and download the free Nippising developmental screening forms. They are a list of yes/no questions based on the child's age with the goal being that should anything be answered no, then it is a good idea to go and discuss this with the family doctor. I do them for all children here and explain to the parents the why of it because children often behave differently at home than in group care and I want them to have information as a progress report for development. I also use them as a tool to narrow down the things that need to be worked on in daycare and keeping a paper trail is always a good idea. Ignore the food issue, as hard as it may be, if his parents don't feed him anything other than what he demands, then there is no hope for you. No sense in increasing his anxiety, if he is hungry he will eat.

As for the younger one, I would take what the parents say with a pinch of salt. Unless she has a cluster of problems then I find it highly unlikely that this kid is in physical therapy and they are just telling you this to get you off their backs. 16 months is still not classified as a significant delay for mobility, many children skip climbing, rolling over etc, and as for talking, she is a second child so doesn't really surprise me. Her eating is learnt behaviour, a product of how she is weaned and as for using a spoon or fork, I really don't personally have an expectation for children that age, I simply give them the option. I wouldn't worry to much about the younger one at this point, maybe come up with a care plan for her to work on these milestones, and for sure do the developmental screenings with her regularly to monitor progress. As for the 4 year old, he is going to JK in September I assume?? Try to work with what you have right now to make the day as smooth as possible. Don't have to great expectations from him as it does seem on the surface that there is more to this than meets the eye. IMO the sooner he gets to JK the better as he will be flagged for sure and have lots more resources available to him.