Ma a fiúval a múzeumba megyünk, mert valahol nyugodtan szeretnénk sétálni.

Hungarian usually leaves out subject pronouns, because the verb ending already shows the person and number.

• megy- = the verb stem “go”
• -ünk = 1st person plural ending (“we”)

So megyünk literally means “go‑we” → we go / we are going.
That’s why you don’t need mi (“we”): it’s understood from the ending -ünk.

The suffix -val / -vel means “with” (comitative/instrumental).

• fiú = boy
• fiúval = with (the) boy

Some examples:

• anya + val → anyával = with mother
• barát + val → baráttal = with (a) friend
• kéz + vel → kézzel = with (the) hand / by hand

So a fiúval means “with the boy”.

Because of the definite article a (“the”).

• fiúval megyünk = we’re going with a boy / with some boy (unspecified)
• a fiúval megyünk = we’re going with the boy (a specific, known boy)

Hungarian uses a / az with specific nouns even when they have case endings.
So a fiúval = with the boy, not just with a boy.

Same reason: a is the definite article “the”.

• múzeumba megyünk = we’re going to a museum (in general)
• a múzeumba megyünk = we’re going to the museum (a particular one we have in mind)

In Hungarian, you normally keep a / az even when the noun has a case suffix like -ba.

The endings are different:

• -ba / -be = into, direction towards the inside → “to the museum”
• -ban / -ben = in / inside, location → “in the museum”

So:

• a múzeumba megyünk = we are going to (into) the museum
• a múzeumban vagyunk = we are in the museum

Here we’re talking about movement to the museum, so -ba is correct: múzeumba.

Hungarian word order is based more on information structure (what’s emphasized) than on fixed S‑V‑O order.

A very common neutral pattern is:

time – companion/manner – place – verb

So:

• Ma = today (time)
• a fiúval = with the boy (companion)
• a múzeumba = to the museum (place)
• megyünk = we go (verb)

This is a natural, neutral way to say it.

You can move things around, but then you often change the emphasis. For example:

• A múzeumba megyünk ma a fiúval.
  Emphasizes “to the museum” (not somewhere else).

Megyünk is present tense, but Hungarian present can also cover near future when the context is clear (like English “Tomorrow we go to London”).

So Ma a fiúval a múzeumba megyünk can be understood as:

• “Today we’re going to the museum.”

If you want to clearly mark the future, common options are:

• Holnap elmegyünk a múzeumba. = Tomorrow we will go to the museum.
• Holnap a múzeumba fogunk menni. = We will go to the museum tomorrow.

But in everyday speech, simple present (megyünk) plus a time word (ma, holnap) is usually enough.

Mert means “because” and introduces a reason clause.

• Ma a fiúval a múzeumba megyünk,
  mert valahol nyugodtan szeretnénk sétálni.

Two full clauses:

1. “Today we’re going to the museum with the boy,”
2. “because we would like to walk somewhere calmly.”

In standard Hungarian spelling, you put a comma before mert when it connects two full clauses (each with its own verb), as in this sentence.
If mert is only linking shorter phrases without a full second clause, there might be no comma, but here the comma is correct and usual.

Both come from szeret- (“to love/like”).

• szeretünk = we like / we love (present indicative)
• szeretnénk = we would like (conditional mood, more hypothetical/polite)

Form:

• szeret‑n‑énk
  • szeret‑ = stem
  • ‑n‑ = conditional marker
  • ‑énk = 1st person plural ending

Typical conditional forms:

• szeretnék = I would like
• szeretnél = you (sg) would like
• szeretne = he/she would like
• szeretnénk = we would like
• szeretnétek = you (pl) would like
• szeretnének = they would like

So szeretnénk sétálni is like English “we’d like to walk”, softer than “we want to walk” (akarunk sétálni).

Sétálni is the infinitive (“to walk”). The ending -ni is the usual infinitive marker:

• sétál‑ni = to walk
• men‑ni = to go
• en‑ni = to eat

In Hungarian, after verbs of wanting, liking, being able, having to, etc. (like akar, szeretne, tud, kell), the next verb is normally in the infinitive:

• szeretnénk sétálni = we would like to walk
• akarunk menni = we want to go
• tudok úszni = I can swim

So szeretnénk sétálunk would be ungrammatical; you must use sétálni with szeretnénk here.

In this clause, the finite verb is szeretnénk.
The word immediately before the finite verb is usually in focus (emphasized).

Current order:

• valahol nyugodtan szeretnénk sétálni
  → the word in focus is nyugodtan (“calmly, peacefully”)

So the nuance is roughly:
“We would like to walk calmly/peacefully somewhere (as opposed to, say, rushing around).”

If you change the order:

• Valahol szeretnénk nyugodtan sétálni.
  Focus is szeretnénk (more neutral: “We’d like to walk calmly somewhere.”)

• Nyugodtan valahol szeretnénk sétálni.
  Now valahol (“somewhere”) is right before the verb → focus on somewhere
  Nuance: “We’d like to walk calmly somewhere (not necessarily here).”

All of these can be grammatically correct; the difference is mostly which part you stress. The original sentence slightly emphasizes the idea of walking calmly/peacefully.