Best style of school uniform for nursery/reception age?

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DD will be starting nursery soon and Im not sure what the best sort of combo is for uniform - skirt, trousers, pinafore? polo shirts or blouses? cardi or jumper?

The school does a branded jumper and cardi then just leaves the rest up to parents - uniform is not compulsory but is worn by about 90 percent of the students.

No idea what the best 'arrangement' to get is?

DS wears polo shirt, jumper and trousers for pre-school which is ideal.

Most of the girls seem to wear skirts though, although a few were in trousers over winter

DS wears grey trousers, a polo shirt/aertex top thing (not sure of the correct name) and a school sweatshirt. There is also a tie but I think a tie for a three-year-old is a bit over the top so he doesn't wear that (I would say about half the children wear one).
Most of the girls seem to wear either trousers or pinafores.
He did go in his normal jumper for a while as he is very attached to it but after a while I was asked to put him back in his uniform jumper.

DS (3) wears playgroup t-shirt/sweatshirt and joggers.

I have sent him in proper trousers before, but when dressing him once he commented that they wouldn't like that, and he wanted normal trousers - I'm guessing someone grumbled in his hearing about buttons/zips on little ones :) so now I just send him in joggers and everyone is happy, he can put them on and off himself, they're cheap, warm, and practical (although I admit they don't look particularly smart)