Hi Sleepymama, in answer to your question about whether reactions stay the same, the answer is no. In particular for milk allergy it can be diificult to predict the strength of future reactions and just because one has been mild, does not mean the next will be. Conversely, a previously strong reaction may not be the same next time.
Generally speaking mild reactions are normally those that occur on the outside (rashes etc), strong reactions are those that occur on the inside (e.g. affecting the respiratory system etc). At this age you should not give piriton (except under medical advice) and in fact the pharmacist may refuse to sell it to you if they realise it is for your lo, but if you notice a strong reaction (problems breathing, distress, facial swelling, tongue swelling, excessive salivation) do not hesitate to call 999.
When your lo starts with the childminder you may want to consider providing your own food. This means you can relax about the childminder not giving food she shouldn't and also allows you to monitor reactions to ingredients (and only send food to the childminder that you have already tried and tested at home first).
The allergy consultant I see with my ds's was very good in giving a list of reactions to look out for and action that should be taken in case of an allergic reaction, which I could give to the nursery (though I admit we didn't send ds2 in the end). It might be worth asking for such a list for your childminder.
Finally wrt proteins in Pepti and Nutramigen, both of these have cows milk proteins in them, but in both cases the proteins are heavily broken down. Pepti is based on broken down whey, whereas Nutramigen is based on broken down casein. Some people react to Pepti but not Nutramigen and vice versa. Some, like my ds2 reacted to both and is now on Neocate which contains no protein (completely man-made mix which is not actually based on cows milk at all!!!). Avoid soya formula though, but I guess you already know that.