sono koinu ha tiisakute, totemo kawaii desu.

When は is used as the topic particle, it is pronounced wa. This is a standard historical spelling rule in Japanese.

So in this sentence:

• その子犬は = As for that puppy, ...

But when は is part of a regular word, it is usually pronounced ha.

その means that and is used before a noun.

The basic contrast is:

• この = this ... near the speaker
• その = that ... near the listener, or something already mentioned
• あの = that ... over there away from both speaker and listener

So その子犬 means that puppy.

Because その is already a word that directly modifies a noun, just like this or that in English.

So:

• その子犬 = that puppy

You do not say そのの子犬.

By contrast, の is used between nouns, as in:

• 友だちの犬 = my friend’s dog

子犬 is read こいぬ and means puppy.

• 犬 = いぬ = dog
• 子犬 = こいぬ = puppy

The 子 here gives the sense of a young or small animal. So this sentence is specifically talking about a puppy, not just any dog.

Normally, Japanese is not written with spaces between words.

So a natural written version would be:

その子犬は小さくて、とてもかわいいです。

Spaces are often added in beginner materials to make the sentence easier to read.

小さい is an i-adjective meaning small.
To connect it to another adjective, you change it to the -くて form:

• 小さい → 小さくて

This is similar to saying:

• small and ...

So:

• 小さくて、とてもかわいいです
• is small and very cute

Here, て connects one description to another.

So the structure is:

• 小さくて = being small / small and ...
• かわいいです = is cute

Together, it means the puppy has both qualities:

• it is small
• it is cute

In some sentences, the て form can also suggest a reason, like because it is small..., but in this sentence it is most naturally just a simple connection: small and cute.

Because です comes at the end of the sentence, after the final predicate.

In this sentence:

• 小さくて is not ending the sentence; it is linking to the next idea
• かわいいです is the final part

So only the last adjective gets the sentence-ending politeness.

A casual version would be:

• その子犬は小さくて、とてもかわいい。

Because かわいい is an i-adjective, and with です you keep the final い.

So:

• correct: かわいいです
• not correct: かわいです

This is different from noun and na-adjective patterns, where です attaches more directly.

とても means very.

Here it modifies かわいい:

• とてもかわいい = very cute

Because it appears right before かわいい, it most naturally applies to that adjective, not to 小さくて.

So the sentence means:

• That puppy is small and very cute

not necessarily

• That puppy is very small and very cute

Yes, が is possible, but the nuance changes.

• は marks the topic: As for that puppy, it is small and very cute
• が marks the subject more directly and can sound more identifying or emphatic

So:

• その子犬は小さくて、とてもかわいいです。
  = a neutral statement about the puppy as the topic

• その子犬が小さくて、とてもかわいいです。
  = could sound like that puppy is the one that is small and very cute

For a simple descriptive sentence like this, は is the more natural default.

No, it is not required.

The comma just helps show a small pause and makes the sentence easier to read:

• その子犬は小さくて、とてもかわいいです。

Japanese punctuation is somewhat flexible, especially in simple sentences like this. The sentence would still be correct without the comma.