I am by no means an expert but I have a child the same age and he seems so different to her and her peers.
He seems in his own little world a lot of the time. Calling his name won't get his attention if he is engrossed in something. He is Toilet trained for wees but most days will just wee and poo himself without saying anything like he just doesn't even notice. He talks but not conversationally if that makes sense - he mostly just repeats what you say or the end bit of a question to reply e.g. 'Do you want to go to the park' he'll respond 'Go to the park'. He doesn't initiate any conversations or try to share anything with anyone even non verbally, it's kind of like he doesn't even realise other people are there sometimes. He has the same little catch phrases and utterances for things but it's like an echo of a previous conversation rather than applicable to the current one iyswim. If we go anywhere he just legs it without looking back - just literally runs into crowds or through resturants/shops. Nothing you tell him seems to really 'go in'. He will have full blown meltdowns anywhere busy like play centres, parties that kind of thing and just try to run out. He's not really that interested in other children and his interactions are mostly just snatching things from them without registering their distress.
He is a really sweet, smiley little boy - loves a cuddle, really affectionate etc but my brother made a comment to me on the weekend about how he thought things would have gotten a little easier by age 3 but they are finding it trickier than ever. I can see he feels a little out of step with other parents and even with me and his neice. My dd had some mobility issues when they were younger so it seemed like they were just concentrating on different things developmentally but now the difference between them is quite stark. Even my DH who is mega chill about this kind of thing mentioned to me yesterday that something seems a bit off with him. I don't want to interfere but we are all close and DB was really supportive to us when DD was having her problems.
I've suggested a GP appointment as that's what I would do but he's a bit reluctant at the moment. Could anyone reassure me that this could just be his normal development or does it sound like cause for concern? Sorry ended up being a long post.