Hello! Watermelon, is a watery fruit, and is one of the fruits that help babies with their constipation. I would suggest you to try apple or pear juice if your baby doesn’t like the taste of prunes. As your baby is 8 months old he can have as much as 6 ounces of juices a day to treat constipation. You can cut down constipating foods like bananas and rice. You can also give your baby a few tablespoons of pureed apples, pears, apricots (they will help loosen his bowel movements). You can also help your baby get some exercises (while he is lying on his back move his legs gently as if he were pedaling a bicycle); and you can massage his belly, below his navel measure three finger widths and gently pressure him with your fingertips. If he doesn’t get better, if the diet is not helping his condition, talk to his doctor about other treatment options. Call his doctor if your baby isn’t eating, loses weight, or has blood in his stool. Do not worry, all babies go through this, especially when parents start to introduce solids to them. I hope, I asked your question. Please, let me know if your baby boy is getting better.