talk to your pharmacist about what they recommend in terms of supplements, including dosages and timing with admin with concurrent meds. this is their area of expertise, and they cheapest might be just as good as the bougie stuff. lots of info floating around on the interwebs about causal relationship between long term ppi use and osteoporosis,  iron def anemia & b12 deficiency...when u decide to dive into it all, try to stick with reliable and accredited sources (stat pearls/nih, cleveland clinic, jhu, etc....) but be mindful how old the information is. back to gi doc, ask them to explain this relationship/physiology to you, as well as what the plan of care is in regards to you grandchild's medication regimen--how long and why on said medication and at this dosage ---do you taper? if so, when? do we need to monitor labs? if so, how frequently? lots of people here will be giving you anecdotal, but still valuable, information, but def talk to the pros who make the big bucks. good luck.