I remember by it being the opposite of English. In English that has the 't' sound. In Spanish this that has the 't'.
Niño/a generally refers to a young child, while a chico/a can refer to anyone young. Like child vs young person in English.
Eso is a neutral pronoun, if you're describing a concept that is not represented by a noun. Ese is the masculine demonstrative.
Ese is used as "that" if you're describing a singular masculine item. Eso is a neutral pronoun for a concept that is not represented by a noun.
'ese' and 'alto' are used for males. So it's chico here. For chicas the corresponding words would be 'esa' and 'alta'. Hence, 'me gusta esa chica alta.'
In my country people say chic just to refer to a girl... En mi país las personas dicen chic para referir a una nina
Why "me gusta" rather than "me gusto" as the remainder of the sentence is masculine?
Gustar is a verb and verbs do not flex for gender. The subject here is "ese chico alto", a singular 3rd person, so you need the conjugation gusta.
Gustar works kind of backwards: the person who's doing the liking becomes the (indirect) object, and the item that's being liked is the subject. You can imagine it as "[Something] is pleasing to [someone]." So "yo gusto" would mean "I am being liked" or "I am pleasing."