If you post what your thinking, I bet you could get dcum to crowd-source plan it for you. I’d help. There are also a ton of very cute pre-made party packages on Etsy if you want something that looks nice for parents—just search “harry potter party” or whatever your kid is into on Etsy and you will find adorable decorations, favors, invites and supplies for party games.
The big question, I think, is whether you want it to be nice for adults or for kids. Sometimes there’s overlap in that but more often not. If you are inviting friends from school, be aware that most parents won’t stay. I planned a lot of cute parties with adorable little themed details that no kid noticed and no adult was there to observe. They were special to me and my kid though, so we enjoyed it. I’ve also done my share of bounce house parties, depending on what the kid wanted.