Maybe they have never heard of the idea and just think you are nuts because
they have never heard of it. Introduce them to this forum so they can learn about more available creative options. Then see what they have to say if you are so concerned about their opinion.
1)Why would you want to use it for children again once it has been converted to a chicken coop?
2) If it has proper ventilation and is kept clean why would a structure with the name kiddie reak any more than a structure with the name chicken? Is their point that it is plastic? Well what about if you use one that is wooden or vinyl?
In my humble opinion, either plastic, vinyl or wood could work fine if cleaned / disinfected regularly and properly ventilated. Bottom line, a structure is a structure. Unless it is a materials issue or a ventilation issue, their point is mute and based on ignorance or lack of creativity.
Now if you want to get a FREE house built by them go ahead. If you really like your playhouse and it has ventilation and access to clean it properly and reguarly, then ignore them. Use your own brain and creativity and don't rely on wives tales or old fashion tradition. If it were me, I would not even have ever discussed my plans with a bunch of air heads. Their ignorance, lack of reason, and lack of ability to think out of the box will hold themselves back and you as well. I would be cordial but make my own decisions without asking their opinion or permission. You are a big girl now aren't you?
PS:
And 3) a structure can be re converted to other uses later, with a gallon of clorox and a gallon of paint. IMO these women have competely illustrated their stupidity and airheadedness all around. Ignore them or educate the. The choice is yours. The bible told me to not cast my pearls amongst swine though so I would keep my pearls of wisdom to myself. By the way the bible also said that God cast demons into swine and we are not to eat of it or partake of it.
( You see I don't think highly of airheads)