Rider intercoms

Speaking tubes are used for some motorcycle intercoms. No batteries or vulnerable tech. Might be worth a search (perhaps try "acoustic intercom").

No more suggestions! I think there's a gap in the market, as I too had this issue when my kids were young.

For anyone with Airpods/Beats and an iPhone, I can confirm the 'Live Listen' feature works. You can plug a wired microphone into the iPhone, I've tested a USB microphone via a lightning-to-usb camera adaptor and a 3.5mm jack microphone a bit like this (yes my phone still has one of those!). So, phone safe in a saddle bag and wired mic to child would do the job, if a bit fiddly.

A set of PMR radios would also maybe work if you get ones with a headset and VOX, which will transmit when speech is detected rather than having to push a button. The parent will need to use the headset, but the kids could probably just have the radio/headset mounted on the child seat somehow. Only problem with those, is your conversation isn't private and other people could transmit on your channel. However, I don't think many people use them nowadays.

For the wind, you could try some cat ears for yourself.

Sena are the market leader in motorbike rider comms, but have some cycling products. No direct experience though and they're not cheap at £85 per person...

https://www.sena.com/eu-en/product/pi

There's also a weird feature in iphone (maybe android too?) where you can turn it into a sort of baby monitor https://www.wikihow.com/Use-AirPods-As-Hearing-Aids possibly lash up external mics to the phone somehow?