Sounds like we are in a very similar situation. I have a very high functioning, but on the spectrum, 8 year old boy whose has a brother 2 years younger and a sister 6 years younger. I am responding to both your post here. Don't worry about the pop culture. It will come. Your five year old sounds exactly like my son when he was five. We got the diagnosis around five and did a lot of early intervention with the school district. The progress has been amazing. Definitely keep him in speech and try to get him in a social skills group. It will help. As someone else said, even as these kids get older, they will need you more to navigate the social scene and how to react. By the way, my 8 year old now defends himself against his brother!
We kept him in sports, even though he was not very coordinated, because he liked to be around the other kids. It has paid off in that this year (2nd grade) he loves being on the team, gets regular exercise and can relate to many different kids because he knows alot about sports. (When he was five he was totally into space and dinosaurs.)
The meltdowns will continue. My child is wonderful at school and other people's houses and saves his meltdowns for us. It is their way of letting go. I have learned that the best thing I can do is to stay even tempered and just ask questions. I found that having a couple of good friends over frequently and monitoring the playdates also helped when he was that age.
Let me know if you have any other issues you want to talk about.
