Бабушка сказала, что манка подходит детям, а взрослым лучше есть омлет или творог.

Because бабушка is grammatically feminine, and in the past tense Russian verbs agree with gender in the singular.

• сказал = he said
• сказала = she said
• сказало = it said
• сказали = they said

So Бабушка сказала means Grandmother said / Grandma said.

Что here means that and introduces a subordinate clause.

So:

• Бабушка сказала = Grandma said
• что манка подходит детям... = that semolina is suitable for children...

This is a very common pattern in Russian:

• Он сказал, что устал. = He said that he was tired.
• Я знаю, что это правда. = I know that it is true.

In Russian, a subordinate clause introduced by что is normally separated by a comma.

So the structure is:

• main clause: Бабушка сказала
• subordinate clause: что манка подходит детям, а взрослым лучше есть омлет или творог

That is why you get:

• Бабушка сказала, что...

This comma is required in standard Russian spelling.

The verb подходить has several meanings, and one very common one is to suit, to be suitable for, or to be good for someone/something.

So:

• манка подходит детям = semolina is suitable for children
• literally, it is something like semolina suits children

Other examples:

• Мне это подходит. = This suits me.
• Этот цвет тебе подходит. = This color suits you.

So here подходит is not about physically approaching; it is about suitability.

Because подходить in this meaning takes the dative case.

The pattern is:

• что-то подходит кому-то
• something suits / is suitable for someone

So:

• дети = children (nominative)
• детям = to/for children (dative plural)

That is why the sentence says:

• манка подходит детям

not

• манка подходит дети

Both ideas can sometimes be translated as for children, but the grammar and nuance are different.

• подходит детям = is suitable for children / suits children
• для детей = for children in a broader, more label-like sense

Compare:

• Эта еда подходит детям. = This food is suitable for children.
• Это книга для детей. = This is a book for children.

With подходить, Russian normally uses the dative, not для + genitive.

Because Russian uses the pattern:

• кому-то лучше + infinitive
• literally, it is better for someone to do something

So:

• взрослым лучше есть = it is better for adults to eat

Here взрослым is the dative plural of взрослые.

This is a very common structure:

• Мне лучше уйти. = I’d better leave.
• Тебе лучше подождать. = You’d better wait.
• Детям лучше спать рано. = Children should sleep early.

Russian often expresses should / had better without a direct equivalent of the English modal verb.

Instead, it uses:

• кому-то лучше + infinitive

So:

• взрослым лучше есть омлет literally = for adults, it is better to eat omelet
• natural English = adults should eat omelet or adults had better eat omelet

This is one of the most common ways Russian gives advice.

Because the sentence is giving a general recommendation, not talking about one completed act of eating.

• есть = to eat in a general or ongoing sense
• съесть = to eat up / finish eating a specific item

Here the meaning is:

• Adults are better off eating omelet or tvorog
• not
• Adults should finish one omelet or one portion right now

So есть is the natural choice.

Compare:

• Лучше есть овощи. = It’s better to eat vegetables.
• Лучше съесть яблоко сейчас. = You’d better eat the apple now.

They are in the accusative case, but for inanimate masculine singular nouns, the accusative looks the same as the nominative.

So:

• омлет (nominative) → омлет (accusative)
• творог (nominative) → творог (accusative)

That is why after есть you still see the same forms.

Compare with an animate noun:

• Я вижу брата. = I see my brother
• nominative: брат
• accusative: брата

But with inanimate nouns:

• Я ем омлет.
• Я люблю творог.

the form stays the same.

А often marks a contrast or switch of topic, while но usually means a stronger but / however.

Here the sentence contrasts two groups:

• детям — semolina suits children
• взрослым — adults should better eat omelet or tvorog

So а works very naturally:

• манка подходит детям, а взрослым лучше есть...
• semolina is good for children, whereas adults should eat...

If you used но, it would sound more like a contradiction. Here it is more of a comparison between one group and another.

Манка is a feminine noun. In this sentence it is in the nominative singular because it is the subject of подходит.

• манка подходит = semolina suits / is suitable

The ending -а is typical of many feminine nouns in the nominative singular.

It comes from взрослые = adults.

Its base dictionary form is:

• взрослый = adult / grown-up (adjective used like a noun)

In the sentence it is plural dative:

• взрослым = to/for adults

Russian often uses adjectives as nouns like this:

• взрослые = adults
• больные = the sick / patients
• знакомые = acquaintances

The basic meaning would stay the same if the word order changed, because the cases show the grammatical roles. But the current word order sounds natural and emphasizes the contrast.

• манка подходит детям, а взрослым лучше есть...

This puts the two groups in parallel:

• детям
• взрослым

That makes the contrast very clear.

Russian word order is flexible, but not random. It is often used to highlight focus, topic, and contrast.

That is the usual English translation, but it is not always a perfect one culturally. Творог is a fresh curd cheese common in Russian-speaking countries. In many learning contexts, cottage cheese is the easiest translation, though sometimes farmer cheese or curd cheese may be closer depending on context.

For grammar purposes in this sentence, the important point is that творог is a masculine inanimate noun, so after есть its accusative form stays творог.