When DD was this age she was fairly indistinguishable from her NT peers.
She was very bright, chatty, big vocabulary. She was confident and outgoing. She went to nursery with no problems, had friends, was well behaved. She played with similar toys to her peers, loved teddies, play food and dressing up.
At home she was VERY stubborn, controlling, argumentive. She had regular tantrums and meltdowns, and nothing would calm her down once she'd started. We just had to wait until she'd burnt herself out. This was the only behaviour that concerned me.
She would talk AT you rather than to you. She struggled with basic social conventions e.g. she had to be prompted to say hello and goodbye, please and thank you etc. When we went to visit people, they'd open the door and she'd immediately launch into a monologue about something random with no introduction or background to what she was saying.
Loads of sensory issues - very fussy eater, hated baths, brushing her teeth, getting nails cut. Hair washing was a nightmare. Terrified of mud, insects, dogs, swimming pools and showers.
Clumsy, refused to walk distances - I carried that child around until she was 6! Very poor fine motor skills. Couldn't hold a crayon properly, couldn't draw or write her name. Couldn't use a knife and fork, spilt her drinks.
Odd interests. She went through a massive Beatles obsession about this age. Magical Mystery Tour was her favourite film 
She'd had random odd behaviour. For instance she's would announce she was going to count to 600 and then do it, and God forbid if you interrupted her 
She was obsessed with door numbers. My mum's house was "number 5 house" not Granny's house - she did this with everyone's house. When we walked down a street we had to check every door for the house number.
Obsessed with colours- everything was a colour, even people. I was white apparently 
So we knew she was bright and quirk, but because she had no trouble making friends at this age, and was confident and outgoing in social situations we were not concerned at all and neither was anyone else.
It all changed when she started school 
She has typical aspergers but her diagnosis is ASD.