Yelling "mom" during the night
My little boy did this until he was about 5!!! Once or twice per night he'd wake up and yell, "MOM!!!" I would nearly fall out of bed in panic each time because I'd be sound a sleep. After a while I stopped getting up and I'd just yell down the hall, "What?" and he'd respond, "I love you!" and I'd yell back, "I love you too!" and he'd fall back to sleep. I really think he was just waking up just enough during one of those light sleep stages to feel a bit afraid and alone and so he'd immediately think of me (because our kiddos are so darn attached to us), and he just wanted to be reassured that I was close by. I know he loves me but I really believe that his "I love you" was really "I need you." He just needed to hear my voice and that would reassure him and he'd fall right back to sleep.
Now that he's 7 and hasn't done this in a long time, it's such a sweet, sweet memory.