Hi, I wanted to ask. My DD is almost 5. And soon we will have a special needs pushchair. When traveling, do the airlines charge buggy as extra luggage? Or it is free, does not included in luggage allowance? Do I need some kind of letter confirming that it is equivalent to a wheelchair? As my daughter's walking difficulties are not visible(she has neuromuscular without a name yet), but people tend to comment that she's not walking because she's lazy.