My son has never had a reaction to a plain hamburger happy meal at McD's.
His specific allergy is alpha-lactalbumin (whey), so others may have a
different sensitivity. Also, we just opt for a sprite or 7-up. I've never
bothered with juice.
And just fyi, I believe their "cones" are dairy free as well, but we've
never had them. We live in the US (Oklahoma).
Gail