I am sorry you are concerned about this claim. The answer to your question depends on whether the legal action you have been threatened with is criminal or otherwise (= civil, administrative, misdemeanor).
If it is criminal, and you have reason to believe you would be charged, then you should indeed be concerned. In such a situation, the best thing to do would be to ask a local attorney in Prague (list of English-speaking attorneys here: http://prague.usembassy.gov/con_am_attorneys.html) to make a formal inquiry with the prosecutor's office, who would clear whether there is any criminal complaint, action, or warrant against you. Please note that a child abduction lawsuit would fall within this category (I am just raising this because some clients do not assume this falls into criminal law, strictly for your information). Also, in such cases, it is possible to have surprises without being notified in advance. So, again, if you suspect anything criminal, it is best to check in advance.
If the legal action is anything else than criminal, such as a civil claim for damages, a family lawsuit etc., then you are safe. Under the European Convention of Human Rights there can be no detention in non-criminal cases, and it is almost impossible for anyone to block you from passing through an airport with your belongings based on such a claim.
If you have particulars about what the claim could be, I would be very happy to further my answer based on this information. If not, I look forward to your rating.
Dr Ioan-Luca Vlad