It's you that's naive to think men can't just walk away from a child here in Thailand. I'm not advocating it's the right thing but I am telling you it's not madatory to support a child you've fathered in Thailand.
you need to expand your horizons beyond De Goorn described as a little village in Netherlands. So, if the laws are the same internationally why are Thais driving on the opposite side of the road to what people in Netherlands do?
Something else to be aware of. Even though the visa has a 6 month validity period it doesn't automatically mean she can stay 6 months. For example. If you put in your application you want her to visit for 4 weeks, she should only stay 4 weeks within the 6 month validity period. If you change your mind for a longer stay after she's arrived I would advise you to inform UKBA. There is no guarantee a longer stay would be granted.