To strengthen the immunity of a 2-year-old, it is worth supplementing vitamin D3 and using a probiotic treatment. However, there are no reasons to give a child vitamin C, just a proper diet rich in ingredients containing this vitamin, e.g. potatoes, parsley, tomatoes or citrus fruits. In pharmacies you can buy preparations with vitamin D3 and probiotics without a prescription. Here you can compare the prices of popular products and order them with home delivery or collection at the pharmacy: vitamin D3: https://www.gdziepolek.pl/produkty/82436/vigantol-krople/apteki https://www.gdziepolek.pl/produkty/39394/juvit-baby-d3-krople/apteki probiotics: https://www.gdziepolek.pl/produkty/107702/dicoflor-baby-krople/apteki https://www.gdziepolek.pl/produkty/90301/vivomixx-krople-krople/apteki https://www.gdziepolek.pl/produkty/117983/sanprobi-ibs-krople-krople/apteki I encourage you to read our article on strengthening immunity in children: https://www.gdziepolek.pl/artykuly/jak-wzmocnic-odpornosc-u-dziecka-przed-pojsciem-do-szkoly and to watch our short video: