Pura I used to buy those fresh in fridge. Though actually not much difference from the UHT, just psychologically think the high heat kills some good nutrients in the box for UHT pack.
Bird nest can be eat continously for a few days, just less than 1 tbsp each morning is fine enough.
Chinese herbal book says just put 蜜棗 in rice and cook together is nutritous for kids to absorb. Please try.