The first one is defiantly underexposed. Your camera's light meter was trying to compensate for the bright light in the background, therefore underexposing the picture. read up on how your light meter works in various modes and you will better understand. Also, for most indoor pics, unless you are using a fast lens, some kind of flash will usually be needed. Try to bounce it off walls, ceilings, etc, to soften the light up. Especially for children, they have very soft skin.