We arrive into LHR T3 from DFW around 7am, and leave for Spain at 340pm out of T5. We'll have 3 kids with us and are looking for a convenient hotel where they can sleep for as many hours as we can squeeze in. Two questions.

(1) what is faster assuming we stay at a hotel near T5 - exiting T3 and taking bus to hotel or taking airside bus to T5 and exiting there?
(2) any recommendations for a hotel, preferably one that offers day use rooms? We are looking at Sofitel and Thistle since both are at T5, but happy to consider other options. Don't need top qualify, as our main goal is to maximize the time our kids can sleep before leaving for the next flight.