Translation:We have a ceremony in the school yard.
Minor point, but shouldn't "halaman sekolah" be rendered as schoolyard (i.e. one word)?
"We have a flag ceremony at the school yard" or "We are having a flag ceremony at the school yard" or "we perform a flag ceremony" or "we are performing a flag ceremony" would fit better.
I think the word 'flag' shouldn't be in the English sentence at all.
No 'flag' (bendera) is mentioned in the Indonesian sentence.
I know that it's usually a flag ceremony that's being held at the school yard, but then the word 'bendera' shoud be mentioned as well in the Indonesian sentence.
The way it is right now, it could be another ceremony.
I've never heard of a flag ceremony before.
Had a Google and just got lots of American results about how to host one, but I've found some Quora threads about Indonesian flag ceremonies, if anyone else was curious:
I just reported "We have a ceremony at the school yard" as wrong because "in" is more natural, but on second thoughts "at" is ok too. So please disregard that report.
I would argue that it sounds more natural to say something is held in the school yard, in the school grounds, in the school courtyard, etc.
Additionally, you could also hold events ON school grounds. As well as on the playground, on the court, on the yard. I think, like with everything in English it seems, it just depends on the context.
I'm wondering if it's (grammatically) correct to use "in" instead of "at".
Using the preposition "in" sounds to me like that you're (halfway) buried in the the school yard.
To me it sounds as if you're knee-deep (or something like that) in the school yard.
Or is it okay in this sentence to use "in" instead of "at" ?
I think it depends on the yard, and whether it's enclosed or surrounded by buildings or not. If you were to say to someone "meet me in the yard", it would be strange if the yard was open-space. You would say "meet me at the yard" or "meet me on the yard". But if it's like a court yard, or a back yard, typically surrounded by other buildings, or an outdoor area in the middle of a large school building, then it sounds more natural to say "in the yard".
I'm not sure about what would be most grammatically correct though.
“At” makes it into a point, “in” makes it into a space. So yeah, since ceremonies need space, I second joeldipops's opinion: “in” is actually so much better that I have trouble accepting “at” in this particular context. Now “wait for me at the schoolyard” could make sense, because unlike a ceremony, you just wait at one certain place and don't move around too much, but because a schoolyard is big, it still sounds awkward. Now “Wait for me at the abandoned kiosk [i.e. in front of it, not within it] in the schoolyard,” that works beautifully. Like Ria_ says, it's all about context.