You can check this brand Biogaia, not sure if they have probiotics for older children though.
I gave probiotics LB30 or LactoGG for digestive system as for vitamin I gave sambucol.
hope this helps https://sg.theasianparent.com/best-baby-probiotics-that-your-child
I fed my LO Scott’s Emulsion cod liver oil to build up their immune system.