My DD1 has a protein intolerance and as a result, as a younger child, couldn't tolerate anything with cows milk or soya milk (or even just soya) in it - she would be really quite poorly. We did a number of visits (3-4 or so) during the time when she was at her worst and I'll be honest, it was never easy - they just don't 'get' intolerances in France - or not imo they don't at DLRP. My DD2 was diagnosed as a small baby and as I was breastfeeding, I had to give up dairy for a year too - one of our trips I was in this situation and I found it hard.
As recommended above, we ate at buffets mainly - Inventions was always a hit - although you need to be careful as they do tend to mix up the meal labels for dishes sometimes which is a total nightmare and really isn't on tbh. We'd breakfast at DLH as stayed there each time and she ate various things from the buffet breakfast - things like egg, toast and fruit. For a while she could tolerate soya and we found that they always had soya milk at breakfast if you asked for it. But then she became intolerant to that too and it wasn't just in milk - it was in all foods - believe me, soya is in nearly everything processed!! We managed but it was always a little stressful at mealtimes! Obviously it's another ballgame when it's two issues to contend with and while we could give our DD pastries at breakfast, that isn't an option for your DS.
I would stick to buffets, and if you get really stuck go for the special meals as a one off. Breakfast is going to be more of an issue depending on where you stay - I'd recommend a hotel providing a hot breakfast if possible, as you can always get scrambled egg (as long as not mixed with cream which is rarely is), bacon and 'proper' fruit if nothing else. I don't know if it's still the case the but the lower budget hotels used to serve tinned fruit - I believe, but this isn't ideal if there isn't much else to choose from. We'd always take a banana or apple for her from breakfast to have during the day and I'd always take snacks from home too - things like organix fruit pots (I'd wrap them in carrier bags and then put in a tupperware dish, then wrap that too, travelled just fine! This was just in case we really struggled, but we always managed somehow!
On the positive, she still has the intolerance but is much, much better now (she is almost 11). She can now tolerate cheese, yogurt and many other things with dairy in - she still cannot tolerate 'raw' cow's milk though as she can't digest the unprocessed protein. She just doesn't have milk when on holiday as most of the time we can't find what she has at home - oat milk. But she still gets her Vit D and calcium intake through the other dairy foods she can now have. She is an amazing eater and will eat anything and everything - we are so lucky as obviously with her start in life, I was concerned.
We've never let her diet issues rule or ruin our holidays but obviously it's not a full blown allergy which is completely different.
I hope this helps - it can be done
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