So what will UK immigration likely say to my american kids
 

So I had a trip planned to go back to the UK to see my Mum and Dad with my american kids and wife. Unfortunately, my wife's chronic medical condition has gotten worse over the last 6 months so I decided that I couldn't go. My two 18 year twins are going to go by themselves to visit their grandparents. This is their first international trip (aside from Canada) and if I am honest I am stupidly beside myself with worry especially as it will be the first time for them traveling anywhere long distance by themselves. I realize that I have to let go, with my kids now adults but it is hard. Anyway, in all the chaos, I didn't apply for the kids to get their british passports so they will be going to the UK on their US passports at the end of this month. I have seen on this website the comment that a person who is foreign born to a British born citizen father (me) is automatically a british citizen. I am going to apply to register their births at the UK Consulate and then get them their UK passports but what I was looking for was perhaps some idea of what my kids should expect from UK Immigration using their US Passports......I mean will immigration automatically assume they are british citizens regardless once they find out that my kids are visiting their grandparents??.. You might think that this is in the realm of things really irrelevant but my daughter is so painfully shy that I am afraid that she will crack and panic when she is asked the usual simple questions from immigration. I am hoping so desperately that that this trip will help to start bring her out of her shell a little (nothing else has worked) and improve her confidence and the last thing she needs is to be interrogated by immigration because they get suspicious of her due to having to pull teeth to get any words out of her.

Re: So what will UK immigration likely say to my american kids
 

Should have no problems if a) they have return tickets to the US b) they say they are visiting their grandparents and c) they are staying for a reasonable time for a vacation ie. 2, 3, 4 weeks.

The authorities won't assume they are British, especially if they have American accents.

I have entered the UK on my US passport without any problems.(I'm a Brit)

Re: So what will UK immigration likely say to my american kids
 

If they are travelling on US passports then they will be treated as US citizens. Standard questions will be asked, purpose of visit, where are staying, how long will be staying, etc.. If you’re concerned (and if you’re very quick) then there’s still just about enough time to apply for their British passports. That way they can pass though the ePassport gates with no questions asked. You should only send colour photocopies of their US passports in case they don’t arrive in time but turnaround times of ten days or less from the US are not unusual.

https://www.gov.uk/overseas-passports