Aziraphale notes Lilly's tightening grasp with slight alarm - this must be a great deal for her to take in, after all - but then Melanie's excitement seems to win her over and he relaxes, letting Lilly join Melanie. He smiles down at them, appreciating once again how well Melanie has taken Lilly under her wing.

"Would you two like to do a bit of exploring?" he offers gamely. "As long as you stay in this area, it's all right." The TARDIS will be overseeing things by nature, and there are several others present. He doesn't want to hover over them. As long as Lilly behaves herself, they ought to be free to have a look, he reasons.