A 7 month old dog undergoes an important phase in his physical and mental development which is called Adolescence. That's the time, he learns to exert his presence in the pack, to understand his territory and so on and so forth. During this period, you notice your dog starting to become alert, his bark becomes thicker in sound, he may get over excited when come across another animal. You may even notice your dog trying to exhert his dominance over the family member by barking at them during play sessions, growling when not being listened to.
This is the time when you have to teach your dog who's the leader in the family.
Does your dog barks and growls only at your daughter or on all family members? If he growls only at your daughter, it means he's not been properly raised. Lack of socialisation right in the beginning makes the dog either to meek or too aggressive. In this case, one must consut a dog behaviouralist. These professionals can correct these behaviour related problems.
If he exhibites this behaviour towards other family members then it's just a result of his mental development. He's learning to defend his pack. However, am not justifying his biting your daughter. Biting is very normal at his stage of growth. You can nevertheless control it in your favour. If he exhibits any aggressive behaviour during play you should do the following- Make him lay on the ground holding him by your hands in such away that your one hand control his upper body including his mouth and neck and the other hand controlling his back so that he's completely overwealmed by you. Hold him in this position until he relaxes and gives in or 3 minutes whichever is earlier. Inthis way, you convey a clear message who's the more powerful and thus the leader in the pack. This will make him understand that his family is not the one he should be messing with. He'll also learn to be gentle with your kids during the play. Repeat this until the symptoms ceases or elso consult a dog behaviouralist.
Secondly, how much exercise you give to the dog? The root cause of aggression is excess energy being left unexhausted making the dogs frustrated which they may express by biting, barking relentlessly, and all other behavioural issues. Infact, Labradors are not the dogs whom you can expect to stay calmly in your house without thorougly exercising them. They don't just require long daily walks but a bit of running.
I've seen people taking their dogs out, after the dog has done potty they take them back to home. That's it. Then they expect them to stay calm all day!!
I wouldn't suggest giving the puppy back to the breeders because when you do so you spoil a life which is bad. A lot of exercise and love will certainly make him a better pet and am sure 100% you wouldn't have to even consult a third party.