From (good article, the whole thing):
Signs of Affection, Age by Age
4 to 6 weeks: Smile. Though it may just mean “Yeah! Here’s my meal ticket!” a grin still signals that your baby knows it’s you.
2 months: Coo. Those first noises are his way of trying to connect with you.
4 months: Laugh. When he giggles, you’ll laugh back, and the interaction delights him.
9 months to 1 year: Hug and blow kisses. They’ll be directed at you, as well as the others in his expanding universe.
18 months to 2 years: “I love you.” Though he’s mostly imitating words he’s heard you say, he’s learning how to express the emotion with words.
Preschoolers and kindergartners: By now, little kids know love is something you feel about someone who thinks you’re special. Preschoolers will rarely say “I love you” to peers, however; they save it for the grown-ups who care for and protect them.
Grade-schoolers: As their cognitive skills develop, kids this age know that love is about reciprocity—and they love those people who they know feel the same about them.
While reading the article, I kept seeing children I have known. I’ve always been struck by the incredible difference I’ve seen in children who were held, stroked, spoken and sung to, and generally loved constantly, consistently, fiercely, gently, and reliably throughout their early years and those who were not. Attachment disorder isn’t just a label when you really see the huge differences.
It really comes down to whether or not those children were loved 24/7/365 by people who were available, present, truly THERE in every sense of the word. You can talk about “Oh, I love my kids, I just don’t have time to spend with them” all you like, but it’s bullshit. Love requires action. It is a verb. It requires your presence. Not just being in the same house or room, but your attention, your energy, your interaction in a caring way.