The way I use "kid/toddler" is in the sense of a child who throws a temper tantrum when they dont get their way.
Like the adc who doesnt get "all the kills" and cries KS over -everything-, then throws a tantrum and talks about how "Trash team keeps ksing me" while they idle in spawn and spam surrender votes.
The adc is acting like a toddler who didnt get the chocolate bar they wanted so drop to the ground to kick and scream and throw a tantrum, making a scene. Distracting everyone else untill they get what they want. These types of children will throw the entire match because -they- aren't the center of attention!
If you act like a child, I am going to call you a child.