ipod touch connects to wifi but wifi apps unable to work

Okay so my daughters's ipod touch (model no: A1367) has had this problem since we got it two-ish years ago. we probably should have got it looked at before but we never thought to. anyway now we're trying to fix it but we can't. BASICALLY, the ipod connects to our wifi, or appears to, however when we try and use apps that require wifi such as facebook, twitter, youtube, snapchat and even the basic ones such as app store and safari, it comes up with an alert box saying 'unable to connect' so although the wifi appears to connect, it must not actually work

what's the problem and how do we go about fixing it?

Thanks

Colin

P.S my other daughter's works fine, and hers was bought the exact same time at the exact same place and my son's ipod touch, which is a lot older (the one without the camera) also has this problem.