One time the allergic reaction may be mild. The next time it may be fatal. Once a person has had an acute non-local allergic reaction to an allergen which the person can not necessarily avoid (e.g. bee sting vs antibiotic), most doctors will automatically prescribe rescue epinephrine. In children who have a history of asthma, development of systemic allergies generally implies a higher probability of future severe anaphylaxis, and the consensus is that these children should have the EpiPen and that schools or guardians should administer it at the first sign of systemic reaction.
The EpiPen is only used as a rescue option for acute attacks, so by not prescribing it for a patient who might need it, you are needlessly risking death or severe anoxic injury (brain damage).
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3666145/
This is from 2008:
A committee of anaphylaxis experts assembled by the World Allergy Organization has examined the evidence from the medical literature concerning the appropriate use of epinephrine for anaphylaxis. The committee strongly believes that epinephrine is currently underused and often dosed suboptimally to treat anaphylaxis, is underprescribed for potential future self-administration, that most of the reasons proposed to withhold its clinical use are flawed, and that the therapeutic benefits of epinephrine exceed the risk when given in appropriate intramuscular doses.
Once a child develops "allergies", most often there are systemic immune changes which lead to increasing sensitivity. Waiting until AFTER the first anaphylactic reaction occurs to prescribe rescue ephinephrine would involve a high risk of death to the patient if such a reaction occurs. Unfortunately, even with correct usage, deaths do occur.
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