Openness when adopting older kids from foster care?

Is there anyone here who has adopted older children from foster care? We are going to be having an open adoption of four siblings through the foster care system. Their ages are 9, 8, 5, years and 3 months old. We live in the same general area as their natural parents.

For those of you in a similar situation, how often and what type of contact do you have with the birth parents?

Some people are telling me that a break in contact is necessary/would be beneficial for the children, to be able to adjust to the situation. They have been living with us for almost two years with weekly supervised visits prior to termination. We have had visits since. Would you recommend a break (several months) and why?

Thanks in advance.