Traveling with 4 year old nephew

I am planning on flying to America this summer, and bring my 4 year old nephew back to England with me for 2 or 3 weeks.

I'm just wondering if since, his last name is different to mine, will it cause any sort of problem? I am planning to bring his passport(obviously) and a form that states his Mothers permission for him be there with me for x amount of time, and his birth certificate.

Im assuming that will all be fine, I'm just worried since there is no father listed on his birth certificate, it might bring up some issues with immigration. I also don't want them thinking I am trying to smuggle him into the country for good since I am here on FLR.

I'm just a worrier when it comes to these things, so even a simple "It'll be fine" will make me feel more at ease.

Any help would be appreciated!

Guidance on Child Visitors: http://www.ukba.homeoffice.gov.uk/visitingtheuk/childvisitors/eligibility/

I would have an explicit letter from his mom stating all the details of travel, in case of an emergency permission for you to be able to seek medical treatment and take him into the UK etc with all her contact information as well. Just to be on the safe side I'd have it notarized and carry his birth certificate and passport (of course). I wouldn't think you'd have a problem.