Si mañana no llueve, llevaremos una pelota, un muñeco y otro juguete al patio.

It is a real/future conditional sentence.

The basic pattern is:

si + present indicative, future

So here:

• Si mañana no llueve = if it doesn’t rain tomorrow
• llevaremos... = we will take/bring...

Spanish uses this pattern for a condition that is genuinely possible in the future.

Because after si for a real future condition, Spanish normally uses the present indicative, not the future.

So Spanish says:

• Si mañana no llueve, llevaremos...

Not:

• Si mañana no lloverá...

This is one of the most important differences from English. In English we also say If it doesn’t rain tomorrow, we’ll..., not If it won’t rain tomorrow, we’ll.... Spanish works similarly here.

Here it means tomorrow.

Mañana can mean either:

• tomorrow
• morning

But in this sentence, the context makes tomorrow the natural meaning.

Useful comparison:

• mañana = tomorrow
• la mañana = the morning
• por la mañana = in the morning

Llevaremos is the simple future tense, first person plural: we will take/bring/carry.

It comes from the infinitive llevar plus a future ending:

• llevar
  • -emos → llevaremos

Future endings are added to the whole infinitive in Spanish:

• llevaré
• llevarás
• llevará
• llevaremos
• llevaréis
• llevarán

Spanish often leaves subject pronouns out because the verb ending usually already tells you who the subject is.

• llevaremos already means we will take/bring, so nosotros is unnecessary unless you want emphasis.
• llover is an impersonal verb. Spanish normally just says llueve for it rains. There is no real subject like English it.

So:

• llueve = it rains
• llevaremos = we will take/bring

Because llevar usually means taking something to another place, while traer usually means bringing something toward the speaker or listener.

In this sentence, the idea is that we are taking the toys to the patio, so llevar is the natural choice.

A rough contrast:

• llevar = to take / to carry
• traer = to bring

English sometimes uses bring where Spanish would use llevar, depending on viewpoint, so this can feel tricky for learners.

Because otro normally works by itself as a determiner and does not take un in standard modern Spanish.

So Spanish says:

• otro juguete = another toy

Not:

• un otro juguete

This is just how otro behaves in normal usage.

Because a + el contracts to al in Spanish.

So:

• a el patio → al patio

This contraction is mandatory in normal Spanish.

A similar one is:

• de + el → del

But this does not happen with la:

• a la playa
• de la casa

Because the si-clause comes first.

When a subordinate clause like Si mañana no llueve comes before the main clause, Spanish normally separates it with a comma:

• Si mañana no llueve, llevaremos...

If you reverse the order, you would normally not use a comma before si:

• Llevaremos una pelota, un muñeco y otro juguete al patio si mañana no llueve.

Because in Spanish it is very natural to use an article or determiner with each noun in a list when each item is being presented separately.

So this sounds normal:

• una pelota, un muñeco y otro juguete

Here:

• una goes with pelota
• un goes with muñeco
• otro already acts like a determiner with juguete

Repeating the determiners helps make the list sound clear and natural.

Here muñeco most likely means a doll, toy figure, or figurine.

It can mean different things depending on context. For example, in some contexts muñeco can also mean snowman. But in this sentence, since it appears in a list of toys, the meaning is clearly a toy figure/doll.

In Spain, patio often means a courtyard or, especially in a school context, the playground or recess area.

So al patio could mean:

• to the courtyard
• to the playground

In many Spain Spanish contexts, if children are involved, el patio often strongly suggests the playground area.

Yes. Spanish word order is flexible, and Si no llueve mañana is also possible.

The version in your sentence,

• Si mañana no llueve

puts mañana early, which gives the time expression a little more prominence.

Both are grammatical, but the original sounds very natural.