Sensibly, a milky tea or coffee once a day won’t do them any harm. I was drinking the same at that age, gradually reduced the sugar and milk when I was 7-8, no health or behavioural consequences then or 35 years later.
Mine are a bit older than yours, but just don’t like the taste, but will drink hot chocolate.
I guess you could even stoop so low as to give them decaf if the caffiene worried you.
Far more concerned by fizzy drinks loaded with sugar. Again mine don’t like the taste or the bubbles, so not a problem for us. Not all kids react to cola the same way, most of my sons mates drink coke, most are fine with it, but they tend to have a balanced diet anyway.
Some parents we know happily chug coke into their little darlings and then wonder about behavioural issues. I have not punched any of them yet for their stupidity, but it’s been close.
As for full on energy drinks in kids, well, it just shouldn’t happen, and anyone who can’t grasp that needs to take a serious look at themselves and their parenting.