You definitely need to consult a local plaintiff's attorney as soon as possible. You have a couple of potential claims here that could result in significant recovery. That is not to say they are sure wins... but they are worth exploring.
1) You have asked about suing the milk companies for a potential products liability action. Here is a brief article on products liability law ... http://topics.law.cornell.edu/wex/Products_liability . Essentially you would need to show that the product was defective, dangerous, or improperly marketed (failing to warn of known dangers). If you can demonstrate that your child suffers from adverse side effects of milk that were known to the company, then you could potentially sue them for damages for failing to properly warn of these potential harmful effects.
Suing the milk companies will be expensive, time consuming, and difficult. However, a seasoned attorney who is experienced in complex products liability cases will be able to give you an idea of your chances for recovery and the risks associated with filing a lawsuit.
2) It is possible that your pediatrician should have caught this problem earlier and warned you of the negative impact milk has on children. Failing to do this could fall below the minimum acceptable standard of care in your area and therefore constitute medical malpractice. Your attorney will want to carefully review the medical records with their own experts to make this determination.
So you need a good lawyer who is experienced in medical malpractice and products liability. The best way to find a good lawyer is by referral (friends, family, neighbors, coworkers, etc)... if that is not possible you can try the phone directory or an online directory such as http://www.lawyers.com/ where you can search by practice area and geographical location. Initial consultations for cases such as this are normally free of charge.
Please reply if I can help further.
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