The primary objective of the clinical trial is the assessment of the acceptability of the new Pentasa formulation - PentasaR Sachets in comparison with the reference PentasaR tablets 500 mg in children with Crohn's disease. After the screening period (which includes medical history, physical examination, basic haematology, serum chemistry , urine analysis and stool microbiology , PCD Activity Index )patients will receive (visit I) Pentasa sachets 1g or Pentasa tablets 500mg for next 4 weeks according to the randomisation scheme in common dose 2× 1 g of PentasaR Sachets 1 g or PentasaR tablets 500 mg. The formulation of Pentasa will be switched at Visit 2, patients will receive the medication for next 4 weeks. Patients will record the acceptability of the both forms of the medication.