A Question from my niece and nephew which i dont know how to answer

18th December 2009, Friday

My niece and nephew asked -

Joey: 姑姑, why baby still dont know how to walk?
Joseph: ya lo, 姑姑, why you DONT WANT to let baby learn how to walk??
Me: remain silent.. **thinking of best answer**
Joey: mummy's friend baby who is same age with janelle is now walking an running already....
Me: really??
Joseph: yes, she can even talk.. why you dont let baby learn??
Me: cos baby janelle is sick, so she is abit slower than normal kids.
Joey: but you see, meimei also sick when she is young, but she can walk and talk when 2 yr old..
Me: Maybe 姑姑 not doing a good job.. can you guys help 姑姑... help 姑姑to teach Janelle how to walk and talk??

I really dont know how to answer them... and this is not the first time they asked me this...