School ties with sweatshirts?

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When DS (10) and DD (9) return to school in September, and DS (will be 5) starts reception the uniform is changing from polo shirts to proper shirts with sweatshirts, and optional ties. Is it worth purchasing ties or let them wear open neck shirts? If without ties, are collars better worn in or out of jumpers?

Ties are work of the devil and should be eschewed at all costs.
Collars - hardly matters. They'll pop in/out of jumpers as the kids move around, and the kids will probably arrange theirs to match the consensus of other kids anyway. Don't worry about it.

Assuming they all want top buttons undone and collars out, which I think could look quite smart, then a loosely worn tie wouldnt be seen really anyway.

Bought them for my elder two as they seem to want to wear them after all