your shots are ok... this is my take on them...
1st portrait.. boy with headphones.. has some spit, liquid or something on his face.. distracting. Easy to clean up in PP.
2nd and 4th shots - need to use a reflector to lighten shadows (as Joe mentioned)
3rd shot - The toy in the baby's face is cute, but I wouldn't use that too much.. distracts from the subject.
5th shot - Man.. eyes are too heavily shadowed... this hides the eyes, which are a primary part of most portraits. Reflector, or light fill flash... or just lighten the whole shot up a bit... there is room to do it.