Can my son 7 years old and 24 kg take sumamed 250mg capsules in this ...

The dosage of Sumamed in children depends on body weight and is usually 10-20 mg/kg of body weight once a day for three days, which in the case of your son means a maximum dose of 240-480 mg per day. So a dose of 250 mg once a day will be most appropriate.

Please note that the dose depends on the severity of the infection, the susceptibility of the infecting microorganism, the patient's condition, age and weight. Therefore, only a doctor can make decisions on this subject, because he knows the health condition of his patient.
Knowledge about age and body weight is insufficient information. Too low a dose may be ineffective and instead of curing, it will only cause bacterial resistance to this antibiotic.

When using an antibiotic, it is worth remembering about a probiotic drug. This will protect your son from unpleasant gastrointestinal ailments such as diarrhea, nausea, abdominal pain.

https://www.gdziepolek.pl/artykuly/probiotyki-czy-warto-stosowac-leki-oslonowe

If you need more personalized advice, you can use teleconsultations here:

https://www.gdziepolek.pl/telekonsultacja/z-pediatra

The availability of Sumamed in pharmacies in Polish can be checked at the following address:

https://www.gdziepolek.pl/produkty/75417/sumamed-kapsulki/apteki