He isn't the best with people, of that he is well aware, much less children, who are really just louder, messier, littler, people. Bag End had never been a place for younglings - his own memories of its halls and gardens reaching back only as far as his tweens - and his parents, dearly departed far too early, had never borne another after him. He had thus grown up with adults, surrounded by their talk and toasting and found them far more enjoyable than the raucous hubbub of overexcited faunts, and he had always wondered (still does) if he had missed some formative life phase wherein one learnt the simple joys of being a child.
In short, he is standing now at the threshold of the round open door, clutching a smaller, softer hand in his, and wondering if he's not just made the biggest mistake of his life.
He knows little of being with children, even less of raising one. Beyond the basics - food, bed, bath, stop them from breaking something - he can scarcely predict what he would be expected to provide his little nephew, and something much like guilt worms its way into his thoughts.
Poor boy, what did he do to deserve being stuck here with his mad old Uncle.
The small hand squeezes, startling him. He looks down to find Frodo staring up him shyly.
"I think I'll like it, living here with you."
He finds enough of himself to smile back with a hum. I very much hope you will, he thinks, and crosses the threshold, remembering the last time he had let a dark-haired blue-eyed being through his front door and into his life.