courts will often favour with you. obviously, children of a young age do not know what is best for them. courts know that it is to be in regular contact with BOTH parents. if you are happy to let this happen, and she is not, then obviously the children would benefit from living with you.
Believe me, in court this happens a lot, so if the children do say anything, it wont influence the judges decision much. Children are often brainwashed by bitter parents. What you should do, however, is document all conversations you have had with your ex and all the times she has denied you contact with your children. If you produce a document which shows eg:
12.1.07 - supposed to see children, ex denied contact
15.1.07 - supposed to see children, ex again denied contact
it would be even better if you put the petty reasons why, for example:
my ex was upset thant my son, 17, has chosen to live with me. as a result of this, she has denied me acces to my other children (plus their ages) on the following occasions:
list all dates.
this should greatly help your case, and if she has brainwashed the children, please do not worry - courts see this all the time. the main thing is to re-establish contact.