Thank you for your kind words, Lymiemomster!
With a 5:1 concentration, I would start off very, very slowly on the herbs and at a very low dose - remember, it means that instead of 1 gram of herb, he's getting 5 grams of herbs. Are all the herbs at a 5:1?
So, for childrens dosages, Buhner says to adjust for their weight and age. Divide their weight by 160 - in his example, he states "if they weigh 40 lbs, you would give them 1/4 the adult dose" - and then adjust for their specific circumstances and symptom picture/response.
Both the Cat's claw -gou teng(uncaria rhyncophylla) - and the Japanese knotweed have antibacterial actions, so he may herx on either of these (as well as the Houttuynia for Bartonella), but Japanese knotweed is mainly for endothelial protection, whereas the Unicaria rhynchophylla is specifically for Neuroborreliosis - Buhner states "If you have neuroborrelosis, it is crucial to add Unicaria rhynchophylla to the core protocol". He only speaks of using the tincture, as a dose of 1/2 - 1 tsp, 3 - 6 times a day, depending on the severity of bran infection. But you can look up one of his suggested herb sources and see what dosage he would be getting and calculate that for the herbs.
That being said, Japanese knotweed would possibly be the easiest one to start, because it's main purpose is to protect the endothelial cells that line the blood and lymphatic vessels. Buhner's suggested dose for the powder is 1 teaspoon to 1 tablespoon, 3 times daily - just remember to divide by 5, as the herbs you are using are concentrated - and to start very slowly.
For the constipation, I would encourage you to get him taking magnesium oxide (to bowel tolerance) or stool softeners (for short term use only) or something. Being constipated only holds more toxins inside of us - besides, it's very uncomfortable and even painful at times (this is one of my worst symptoms).
Do be sure he is doing all you can get him to do for detoxing as well. This will be very important to get him through treatments, no matter what form of medicine is being used. If you need ideas, you can go here:
www.tiredoflyme.com/detox-methods.html or ask! I know one mother that created jello shots to get meds down her child - and the last I heard, it was working!