He or She for animals of known sex?

Yes, as long as you know the *** of the animal - and this means the animal is some kind of pet to you, well, if a lion lets you see whether it's a male or a female, you must get along pretty well! -, it's no longer a "it" but a "she" or "he"

Okay, thank you, pieanne!
The problem, I think, it won't be with lions or big animals, the problem is with frogs, spiders, and such kind of little animals.
By the way, please, would you be so kind to tell me (I'm a native Spanish speaker) how it is used to naming in English diminutive persons, animals or things (only by using “tiny” or “little”, etc) – and what about enlarged persons, a

Well, in the case of frogs, spiders and all these lovely animals, I guess the safest way is to use "it". If you have to make a diffe

The diminutive suffix is "-y", and it is of very limited use, chiefly in the talk of children, and almost exclusively with one-syllable words, as far as I know. Sometimes other changes occur simultaneously with the addition of "-y".

frog - froggy
dog - doggy
horse - horsey
mouse - mousey
cat - kitty

Robert - Bob - Bobby
Robert - Rob - Robby
Leona

Just one more I remember: duckling for a little duck.

Duckling is not just a small duck, it is a baby duck.

Thank you all of you. Now I know there is no rule (suffixes) in English, as in Spanish is, to talk about diminutives. But you said nothing about "aumentatives": (animal, animalón; where "on" is the Spanish suffix which stands for "very big animal") in English. Have we to use adjectives "big"; "large", "long", etc?
Could you answer to this, please?
Eladio

No augmentatives in English, beyond the adjectives-- but lots of those: big, large, great, enormous, immense, huge, humungous, colossal, stupendous, gargantuan, tremendous, gigantic, monolithic... (to compensate for the lack of affixes, perhaps)

'Spiderling' exists; but it's used for a young spider, rather than a small one.

For frog, you could use 'froglet'.

Once there was '-kin' (lambkin, Peterkin, etc), but it seems obsolete now.

Curious that no augmentative suffixes seem to exist. I suppose we can use '-issimo' or '-meister' for human activities: generalissimo, verbmeister, etc.

Or the 'mega-'

All this is very interesting, and all of you have been very kind with your answers. Thank you. Now I'm asking myself if my city is "a very big city" or a "citykin", and if my attic is "very very wide" or it is "an atticy" (-y). But anyway I can say EnglishForum is a "forumissimo" very useful for me. It's just a comment-joke!
Eladio