Yes, three hours IME.

It depends which gate as to where you may want to go.

They quite often go from gates 5 thru 9 (turn right after security/immigration), in which case the Qantas Lounge would be my on target.

However, they also quite often go from further down the terminal. There is an Amex Centurion lounge around gate 60. This is mid-terminal. It can get busy, although I've not seen that situation post pandemic. It is a bit of a walk, probably a good ten minutes with kids, but you can take the transit, which might be exciting for the kids anyway.

The only Cathay business lounge in HKG I've been in since the pandemic is the Deck near gate 6, so near the Qantas Lounge. I would choose the Qantas Lounge over the Deck.

I've only tried to get into one of the Priority Pass lounges, the one around Gate 60, which was to get a shower because the showers weren't working in the SIA lounge (I was on Swiss). It was a zoo, so didn't bother. They do seem to attract long queues outside, so I wouldn't guarantee you'd be able to get in. Thankfully my Swiss F ticket also allowed me access to the Plaza Premium First lounge where I got lucky and had a shower immediately, but I don't think that's on Priority Pass.

There is a new Chase lounge next door to the Amex lounge that looks like it's on Priority Pass too, but I've yet to try that.

My own favourite lounge at HKG is Pier F propping up the bar, but it's a bit of a trek and not really particularly child oriented, and ISTBC but from the information given I don't think you have 2 OWEs travelling?