“I have my first patient now (2 1/2 years old), he goes to a special school, other kids see that…other parents see that, and will come to me, I´m sure that in a few months I can´t handle all those kids on my own, so I have to hire people then…”
You say you don’t work with children, but to clarify the above, how is it that you have a patient? Do you not mean customer? Also, if you’ve sold the prints to one child, or even a dozen or more, how will you make so much money to hire other people? It does not seem to be that kind of business unless you charge a lot for the prints!
“and I know that it is important not to infringe the copyright for a profit business. That´s why I ask it, you don´t have to do it, off course. That will be okay for me, I can draw too
And…most kids want cars, or for example, this kid wants Bob the Builder on his legs, there are a lot of free pictures on the internet which I can use for this kind of wishes.”
Yes, copyright is an issue here. You must realise that in your example given, the Bob the Builder character is subject to copyright and you would need permission to sell anything with his likeness. However, if you use your own drawings there’ll be no problem. Have you any examples that you could show us?
“And do I plan to make profit out of your art, I think I don´t do that, because I want to respect your rights, and so I ask people this question, if you don´t want to, you don´t have to. It´s just a question, and if there are people who want to make a drawing especially for the kids, or want to give me one or more pictures for use on those legs, it will make a lot of people very happy, yes me too off course, but for me, as I told I draw too, I will have a lot of work, drawing and making nice drawings then when I start with this.”
But clearly you do plan on making financial gain from the art that is given you, otherwise there would be no business sense in it. Basically you are taking the art to sell to the amputees
“The amputees theirself have to pay me then.”
Who are paying you a sum of money in return (as you say in the quote).
“Let that bell ring!! It is good that you ask those question because I don´t want problems either. Maybe i am thinking to simpel about copyright, that can be true, and if i make a mistake here, you may tell me so. Then I shall tell a mod to delete this message, no problem. But because i draw too…i really don´t want to abuse the rights from artists…There is already too many things stolen on the internet…and I hate it too, it hurts me too when I see that an artist has given up his homepage because of the stealing.”
“and maybe in the future I can talk about contracts or something with the artists, I really don´t know that yet at this moment. But what I am planning to do, if someone has given my some pictures, then if i used them, they will receive some photos.”
Yes, I think you should reassess your business plan, if you are not absolutely sure about copyright! There must surely be bodies which you can approach for advice in Holland about this, particularly on legal matters and drawing up a contract?
As you are asking artists to donate their art for the good of these children, you could consider a possible link up to a disabled charity, as a more appealing idea than the commercial route you are taking.
Regardless, it would be better to get things clear before you enter into any agreement on line. Artists may be concerned as to what they are actually agreeing to. Allowing a stranger to have an open ended and unlimited access to all their work in a gallery for commercial gain, without any money going to the artist, is not wise without a contractual agreement.
Of course any artists agreeing with you on this, it is their prerogative. 
But in any case, feel free to use any of my pictures posted here at ZBC for this specific purpose.