This was a supremely bad idea. Neville had been considering this move for a while, but with Harry spilling the beans to Moody and then subsequently the Order finding out that time travelers were in fact there, he couldn't really put it off much longer without seeming like he didn't want to see them. He did, he really did. He was just nervous. The image he'd built up in his head was something that no real person could live up to, so Neville had steeled himself for lowered expectations, then realized eventually that he would be happy with whoever they happened to be, so long as they were alive and sane.
When he heard his mother was in St. Mungo's, he figured this was the chance he needed. They wouldn't attack him in the hospital, and now that they knew about Harry at least they were less likely to consider it. So, he sought out his mother's room and was both pleased and terrified to find them both there. He knocked on the frame of the door, waiting for either permission to enter or the inevitable 'who the hell are you'?