it isn't always that simple, sometimes the kids have to get into a school environment to realise something is wrong, and then you get all the professionals around you going 'oohhh, they'll grow out of it' so you wait, and they don't, and then you have to get pushy about referrals.
my DS initially presented with things like a speech delay, but then within a few weeks of being at nursery for his free hours aged 3, was talking fine. He was a fussy eater, didn't like getting wet.. looking back, clear sensory issues, but no-one flagged it and when i flagged it, just told me it was normal for toddlers and he'd grow out of it. He didn't.
Then when he did get to school, they still weren't flagging autism, he was diagnosed with dyspraxia first at 7, then autism/sensory processing disorder & ARFID at 10, and adhd 2 months later (same dr).
I would love for him to have got that diagnosis earlier, but not one person listened to or believed me, and it isn't much better now.. having been through it with DS, i've been fighting for DD who is blatantly also asd/adhd and at 15 and in her gcse year, only just been paid attention to, because, guess what, she's failing BADLY, because no-one thought it was an issue, as she was 'coping' outwardly, and she was, until she wasn't, and now the shit has hit the fan.