He plays really well with girls and not at all with boys.
His siblings are the exceptions- Maryn and Jonas have never gotten along that well, mostly because she doesn't let him play with her or her toys. He loves playing with Seth, but as with most older brother/younger brother relationships, Seth starts getting impatient and annoyed with Jonas after a while.
Girl example #1: Jonas thinks his best friend is Zoe (pictured above as the white queen with her little sister along with Maryn and Jonas) even though Zoe is Maryn's age and her best friend. To Zoe's credit, she balances these two kids vying for her attention with way more poise than you would expect from a five-year-old. Because Maryn is in kindergarten now and Zoe is not, she and Jonas have had a lot more opportunities to play together one-on-one and they both love it. I sometimes think that Zoe prefers to play with Jonas... I'll never tell Maryn though.
Girl example #2: C and her mom came over last week and spent two hours with us one afternoon. C is the youngest of 4 and only about two months younger than Jonas- they're in nursery together at church. Their whole family has been to our house numerous times, so this definitely wasn't the first time they had played together. So this past week, for the entire two hours, they played and played and didn't make one peep. Not one fight or complaint or tattle, nothing. I was shocked and amazed. And this is when my theory started brewing because of the following two examples.
Boy example #1: W moved in next door to us at the end of the summer. He loves to play with "Jona-th" and is always so excited to have Jonas come over to his house or play in our shared backyard together. I think the part of the relationship that Jonas likes the best is being able to play with W's toys which are cool in his basement playroom which is way cleaner than ours. He doesn't ever seem all that interested in actually playing with W.
Boy example #2: I have arranged with a mom of one of Seth's classmates to have weekly playdate swaps with our three-year-olds. L is a pretty easy-going kid. But when he comes over to our house for the playdate, Jonas is upset the whole time- crying, telling L not to touch his toys, refusing to play what L wants to play. This means that I have to spend the whole two hours hovering, trying to make sure that Jonas shares and doesn't cry or say mean things to L.
I don't know that it means anything, really. I think he likes playtime with a structure or creative "purpose" and maybe other three year old boys just don't play that way. I'm cool with that, generally playing with girls is quieter.