More neutral:
* Complaining
* Gripe
* Fussing
* Moaning
* Grumbling
More negative:
* Bemoaning
* Kvetching
* Whinging
* Grouching
* Pestering
* Nagging
* Tantrum
* Crying (if it's a child)
More specific:
* If it's about something someone is owed: Demanding, pleading
* If it's about something someone doesn't like: Objecting, disagreeing
* If it's about something someone is afraid of: Fearful, anxious
* If it's about something someone is hurt by: Sad, distressed
The best word to use will depend on the specific situation and the tone you want to convey.