Some kids are like that... it does not mean they are OCD.
Both my kids... get like that sometimes, and especially when they were certain ages.
Keep in mind, that there is ALSO age-related "rigidity" in habits, that develop... but it is PER the age set of a child. I even read that in a book on child development. It is about the child doing that because it is an age stage... and a child's way or organizing the world.... and keeping it predictable etc.
Next, some kids do this because:
1) it is a coping mechanism... for other stresses in their life etc.
2) They do it because they do not, at this age, have natural ability for "coping" with things... thus, they may do things like this as a way to cope with stresses/worries etc. that they have.
3) They do not have any other way to express themselves, so it gets displaced onto other things.... hence, even a banana
4) They at this age and younger.... do go through a stage of being detail oriented and "organizing" things in order and "sequencing." Both my kids did that too. ie: putting alike toys all in a row and by size and color, for example. But its normal.
He is very young....
how is his OVERALL development and communication skills and ability to express himself? Maybe he is the type that is not as able with those things? But you can work with him on it.... boys, need to learn how to express themselves... it is very important.
Anyway, I think he is young to definitively be called "OCD."
My kids are not... and they have done some of the things you described, about your son. My kids are normal kids and VERY expressive. So well its a loud house sometimes! LOL
The thing is... I would maybe teach your son, or guide him, on 'coping skills.' So that he can understand that there are MORE than 1 way of doing things... sometimes. Also, some kids cling to doing things a certain way... because it is comforting.
See if you can talk to him about it too.
I used to ask my kids, with a nice voice, "Why does it have to be that way?" And well, they would give kid like answers.... which to them sound legitimate. But to me, made no sense. Kids.
My kids per their ages now, are not really like that anymore. It was a phase.
Or, get him assessed... an OVERALL developmental assessment.
Maybe he is borderline something... who knows.
But at the same time, 3 year old kids get like that. Mine did. They are moody and tantrum. They cannot 'control' their world or what they want or don't want and they do NOT have the "skills" to completely have ability to navigate their world.
But you said your son is like a "switch." He seems to have a hard time dealing with things.
Your child seems VERY structure oriented and cannot 'cope' perhaps, with anything else. He "NEEDS" patterns and routines and sequencing... or it irks him.
I would try and teach him or help him to learn... about other rhythms to life... to situations. Maybe once he is not 3 and older, he will become more pliant...
All the best,
Susan