I just don't know how you could forget a baby. My older children would have surely reminded me .
Ten years ago when my third child was four or five years old, we all took off in our van to pick my mother-in-law up at the airport. I had four kids at the time. We were halfway there and my oldest son (age 10) said, "Where's Mikey?" WHAT????? It took him that long to realize he wasn't with us? That was before we all had cell phones, so we couldn't call the house to reassure him. We ended up driving back only to find him sitting at the computer playing a game. When we told him that we'd all left without him, he said, "Cool! It's like Home Alone!"