Le bébé mange tout seul.

French normally uses an article before a singular count noun, so le bébé is the standard way to say the baby.

English sometimes drops articles in places where French does not, but here French needs one.

Not necessarily.

In this sentence, le goes with the noun bébé, which is normally treated as grammatically masculine. That does not automatically tell you the baby's real sex.

So le bébé can refer to a baby boy or a baby girl, depending on context.

Because the subject is le bébé, which is third person singular.

The verb manger in the present tense goes like this:

• je mange
• tu manges
• il/elle mange
• nous mangeons
• vous mangez
• ils/elles mangent

So with le bébé, you use mange.

It can mean either one, depending on context.

French often uses the simple present where English might use either:

• eats
• is eating

So Le bébé mange can mean either The baby eats or The baby is eating, depending on what is happening in the conversation.

Seul by itself means alone or on one's own.

Adding tout makes the idea stronger and more idiomatic here. Tout seul is a very common expression, especially with children, and often suggests all by oneself or without help.

So tout seul sounds very natural in a sentence about a baby doing something independently.

Because this is the expression tout seul, where tout is not the plural form of all in the usual sense.

Here are the common forms:

• tout seul for masculine singular
• toute seule for feminine singular
• tout seuls for masculine plural
• toutes seules for feminine plural

So in your sentence, tout seul is the correct form.

Often, yes: the last part may change to feminine.

You may hear:

• Le bébé mange toute seule.

That is because seule refers to the actual child, so speakers often make it agree with the baby's real sex.

But bébé itself is still commonly introduced with le. Some speakers may avoid the mixed look of le bébé ... toute seule by using another noun instead, such as la petite.

Because it is describing how the baby eats, not directly forming a noun phrase like a lonely baby.

In Le bébé mange tout seul, the phrase tout seul works with the verb and means something like on his own.

This is very normal in French:

• Il dort seul.
• Elle travaille seule.
• L'enfant mange tout seul.

If you put seul directly next to the noun, you get a different structure and often a different emphasis.

The accents é tell you that the vowel is pronounced clearly, roughly like ay in English, though the French sound is not exactly the same.

So bébé is pronounced approximately bay-bay, not like an English silent e word.

Those accents are important. Without them, the pronunciation rules would be different.

A rough English-friendly approximation is:

• Le ≈ luh
• bébé ≈ bay-bay
• mange ≈ mahnj
• tout seul ≈ too suhl

A few useful pronunciation notes:

• the final -e in mange is silent
• the final t in tout is silent here
• French does not use stress the same way English does, so try to keep the rhythm fairly even across the sentence