Very young babies do not have the digestive maturity to deal with prune juice. At 10 days old, the baby may still be passing meconium and the bacteria which will aid digestion of solid food is only just beginning to colonise his/her gut. The best and indeed only necessary food for a baby of this age is breast milk. If this is not possible, then an appropriate formula milk, made up according to instructions, can suffice. As I said before, if the weather is hot then extra water can be offered between feeds. Nothing else should be given for at least two months, preferably longer.