Currently in Vietnam and agree with your comments. My daughter did not like Thailand especially Bangkok and has no great desire to return. But has loved Cambodia, Laos and Vietnam.

We’re quite happy to use pool rather than beach and from what I can gather the southern beaches/islands of Cambodia and Vietnam all have trash issues. Only beaches we’ve visited so far were Halong Bay. You would not want to go in the sea there as you would come out covered in oily brown slime! We’re about to head south so will see how things are there shortly.

As others have said, cutting down your itinerary is probably a good idea - less is more. Fortunately we're flexible, but have already cut back on destinations. You can spend an awful lot of time waiting for buses, taxis and trains as well as at airports. If you get your timings wrong, you can waste the whole day. Have also had lots of delays to flights - doesn’t seem to matter whether it’s Singapore Airlines, Vietnamese Airlines or a budget airline. That could change by the time you travel.

Who knows whether BA will return to Bangkok. But there are always likely to be flights to Singapore which makes a quick hop over to Malaysia very quick and easy and much more doable with small children than Angkor Wat.