I have never had malaria several times, but the ones I had when I was a kid, I will respond base on my experience after it was confirmed that is malaria.

How do you know when you start to get malaria?
My answer:  You feel dizzy, tired most times and lack of hungry for food

 How can you tell that it is malaria and not, say, a flu or a cold?
My answer: Through lab diagnosis

 Are there any specific symptoms which might even be very subtle so that you are able to differentiate? Or do you recognize it from how it felt when you had malaria as a child?
My answer: As a kid I will like to seat on the sun, sometime vomiting; and sleeping than necessary.

Do you maybe recognize it like you recognize a face or a voice?
My answer:  My eyes sometimes change to yellow like color and I become slow in talking.

Sorry- I was carried away by other activities in Cokoye and just see your reply.

My parent starts treating malaria when they saw that the malaria is coming by observing and seeing symptoms I listed above but most times, I do hide it from my parent (because I don't like taking that bitter drugs and injection) until I get undulating fever that I can't hide it anymore. But it's always advisable to start treating malaria from the onset.

You're second question can be found in the no2 of my answer. Because 98% time I don't go to lab to know it's malaria, I just know by the signs I indicated earlier.