Hi Claire
Our daughter was 4.5 when we started fostering, now 6.5, we had always been honest with her about what was going to be happening, (maybe too honest,) we did focus on the fact the Lo's coming to us, need our love and that the things they do may not always be how we do things.
She has coped really well, that's not to say, she does not get fed up, angry, upset with the boys, (they are 5.5 and 3, currently been here for 2 years and challenging!) She rejoices in their achievements and honestly does love them.
We do try to spend 1 2 1 time with her, and she does retreat to her bedroom, (this is a no visitor/boy zone, unless asked).
It would just be apprehension on what's going on, that the changes in behaviour are coming out as. you will be nervous and they do pick up on that!!!
i am not sure holding off would solve anything,
Our next battle will be when they move on! this is due to happen later this month, as they are going to meet their' forever ' mummy and Daddy.
Good luck.
Pm if you want.
Kiddiwinkles