Sounds that make me nervous

There are two "sounds" that make Derek and I a little nervous when we hear them:

• when the girls are playing upstairs or in another room and we hear a loud thud followed by Winnie saying "she's okay mommy"
• when the girls are playing upstairs and we go to check on them but are instead greeted by Ellie at the top of the stairs saying "no mommy, you don't come up here, you go back downstairs!"...makes you wonder just what exactly is she up to?????