Hi A.---I have a friend, when having lunch together, gave her 1 year old daughter the lemon from her water to suck on. I say go for it if he likes it.
I am also taking wellness classes, taught by a Naturopath who has her PhD in Nutrition. I have a number of books talking about the nutritional and medicinal properties of different foods. I was really surprised to learn that bananas are recommend FOR constipation. When my husband broke his hand and collar bone and had problems from his pain meds, I gave him bananas and kiwi with a bit of agave nectar and it really helped him resume normal bowel movements. Does your son drink lots of milk/dairy? Dairy is one of the most constipating and allergenic substances in the world. That's because cows milk is designed specifically for baby nows, NOT HUMANS. Please go to www.pcrm.org and put dairy in the search box. Two other sources are www.whynotmilk.com and www.thechinastudy.com. Check it out.
For constipation, be sure you are all eating high fiber foods and drinking lots and lots of water. Reduce and/or elimate processed foods as they contain little fiber. A balance diet of fruits, veggies, whole grains, legumes and nuts and seeds will make elimination a breeze. And that's important as the longer that stuff is in the gut, the more toxins and bad stuff the gut reabsorbs. Feel free to contact me if you'd like to discuss the points I've raised. l feel that our medical system does not understand the healing and preventive powers of food and that they are doing a disservice to their patients by not starting there.
Good luck...have fun introducing...and reintroducing new foods to your family's diet. In health, D.