To be unsure about DS going to this party?

Aw, that sounds nice! Excluding him would be not inviting him and saying that they assumed he wouldn't like it cos he's a boy. Anyway, there're tons of options for male Disney characters. I'd go for the Beast, as he looks quite prince-ish so won't spoil the theme, but he can have a Beast mask to put on if he feels it's too "girly".

I think you might be letting your gender prejudices manifest a little. He’s 4, let him have fun at the party, most children love a party. Most boys like to play princess given the chance as well as other ‘girly’ things. They like what ever their friends like (and in turn what their parents have moulded them to like!). Let him have some childhood fun, he will have the rest of his life having to live up to gender expectations.

Honestly, you get more paranoid with every post.
Why do you think they don't have "free choice"? This is nuts.

I know this will make little sense but I feel they like DS as an individual but not as a boy. Very hard to explain! And I feel as if the princess party is almost a way of excluding him: a sort of well, you can come but you aren’t really welcome?
Yeah, it's hard to explain because it doesn't make any sense.
The birthday girl has chosen a theme without any reference to your son (as she should ) and he hasn't been excluded anyway.

If a lot of his friends are girls these are the sort of themed parties they will have. I'm sure it will be fine whatever he wears and he will have a good time. If some mums of girls think boys are a bit rough so be it, but so are some girls.

Oh my DS would adore this! Yes by all means get a Prince outfit if you can. The girls DS plays with are obsessed with him being a prince when they play princess!

I think you're overthinking it OP.

And I feel as if the princess party is almost a way of excluding him

You think someone planned their child's party theme (a very common party theme) around sort of making your son feel unwelcome?

Kindly, this is ridiculous.

He could be a knight?! Or just stick him in his favourite superhero costume or whatever. Kids don’t really care that much. I’m sure he’ll be happy to be dressed up and at a party!

What’s your concern here? It’s unlikely any of them are going to grow up to actually become princesses tbh…

My daughter only had one boy at her party (when she turned 5). It wasn't a princess party, granted, but he was her pal, she wanted him there, and he had a great time playing with the girls.

@leavehimthere in the nicest possible way you are massively overthinking this.

Boys are more boisterous. I roll my eyes at my own son.

Long discussions about hair styling? Me and my SIL literally paid for a hair styling class our DD were so desperate for the perfect Elsa plait.

The vast majority of little girls have Princess parties at 4 years old- totally normal.

I think this is a you issue tbh unless there’s a massive drip feed coming.

He's not being left out or excluded. Yes it is unfortunate he is the only boy in the group, but would you have preferred them not to have invited him at all? At that age i'm afraid girls are going to potentially do the princess thing (and potentially when he goes to primary school too, this is when my daughter had her princess party and invited boys). I don't see why they should choose a different theme to be inclusive for your son.

My son has been to two of these and was the only boy both times. He was for the second time. He absolutely loved it both times. He went as Olaf as one of the princesses was Elsa. Apart from there being princesses there it is a normal party with games and music like you would normally have and the the tea party was a bit like what they had in Alice in Wonderland so he thought it was fab. They also had a slide that they got to play on. At no point did he seem the odd one out of pushed out apart from his costume that everyone loved and he thoroughly enjoyed it. I think it's a good thing to do when they are young as older boys I don't think would enjoy it unless they like princesses.

Hans or Olaf costumes are available if DS wants to dress up differently to the Princesses.
Males can sing and dance equally as well,with as much joy, as females.
I'm not sure there is an issue here, unless you make one.

Is it a party for all of their birthdays, or a party for one of the kids?

He's 4, it's a party, he will have fun. Let him wear whatever he wants, at that age my son would have wanted to wear a princess dress too. And stop getting hung up on him being the only bit in the group. My DD was the only girl in ours and it made no difference at all.

If he wants to go, why not let him dress up as a mouse or a cat or whatever he wants. I know someone who does these parties and it is more about dressing as a disney character than a princess.

And just let him wear whatever he wants to the party - one of my DDs is anti princess and would probably want to wear a superhero costume and that would be fine.

Agree he's not being pushed out at all, he's invited.

It’s not the first time he’s been sort of subtly pushed out and it makes me a bit sad for him.
I am not sure what you mean as he is being honoured as the only boy with an invitation. He is being very much included!

If he doesn’t happen to want to be a princess he could be a wonderful prince.

If you don’t think he'll enjoy it, I would invent a convincing reason why he can’t go. (But it will need to be something that he believes too, or he’s bound to give the game away.)

But I don’t understand why you think he’s being "subtly pushed out". The reasons you give sound ridiculous to me. But if it worries you, perhaps try to get friendly with the parents of a crew other boys, by setting up play dates etc.

The party theme is whatever the kid whose birthday it is, wants.

Send him as Prince charming, as a disney princess or as the hulk. Whatever he wants to wear. He'll be fine.