The children were seized by social workers after the three youngest had been left in the care of their 17- and 15-year-old siblings while their parents were on night shift.
Mr Hemming is in touch with other foreign governments similarly concerned by the way their subjects are being taken into state care in Britain for reasons they believe to be in breach of human rights laws.
The Slavic majority and Hungarian minority in Slovakia are embroiled in a bitter dispute over language that is spilling across the border.
Nowhere in the European Union are relations worse between neighbors than those between Bratislava and Budapest.
The demonstration was timed to coincide with a hearing in the London Court of Appeal of the plea of a grandmother, supported by the Slovak authorities, to have her two young grandsons returned to her care in Slovakia.