Soy milk and... Soy milk, chicken, and fish would be good sources.
Alternatives. Soy, oat, almond, coconut, rice and hemp milk. Taste and nutritional value vary with these, so make sure you read labels and try to purchase fortified options. Some children with dairy allergy can tolerate hydrolyzed formulations. You should discuss this with your child's pediatrician.
True allergy rare. True milk allergy is rarebut dramatic, I have seen lips & face swell within minutes. If so, avoid & substitute. U can get the calcium from crushing a tablet or finding a milk substitute. Water is a great fluid for the older kids, fat & protein from other foods. If your kid is just lactose intolerant (1/4 will be) then avoiding lactose is your goal. Clarify with your dr, the goal should match the pbm.
Allergy evaluation. All who have been diagnosed with milk allergy should see an allergists to clarify the clinical symptoms of milk allergy. If an allergy or ige antibody is felt to to be the cause then skin testing and / or blood testing should be done. Assuming there are no other food allergies and this is ige mediated reaction then soy milk could be substituted.
Doubtful. Intussuception is most commonly associated with rotavirus vaccine. Milk allergy has many symptoms in young children but Intussuception isn't one that I have seen documented.
See doctor. If indeed this is an allergic reaction, seek medical help immediately.
Avoidance. Avoidance is key. If your child is already having symptoms of cough and nasal congestion, you can give an antihistamine: benadryl, (diphenhydramine) Cetirizine or loratidine at the right dose (check w/ doctor). If your child is having shortness of breath and wheezing, you will need a breathing treatment which can be prescribed by your doctor. If you need to confirm allergy see an allergist for testing.