Kids below 14 don’t get fined for overstays but I suggest to do the visa for your child. You can get further visas requests being refused/ have tons of questions at the airport…. Spare yourself a headache.
It depends of the embassy some will ask 500 000 for each or 500 000 for all. Write to the embassy you consider to apply to make sure. You will still need to pay fees for 4 people
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