Good luck. It will be fine. (((hugs)))
Mine found out 5 months ago, and are the same ages. They really took it very well and accepted it. I still get "I want my daddy" and "why doesn't daddy live here any more", but emotionally they are little troopers.
There was some little behaviour issues, but they have mostly gone now. What I did was tell my eldest's teacher and she watched out for her behaviour in school too and told me what was going on (a bit of regression and attention seeking), they also did "art therapy" in school with her (drawing and chatting about the picture), I think with that she just loved the attention, as it lasted 10 weeks of 1:1 with another adult. I have made sure they have lots of contact with other adults and they are enjoying that, as it is more stability.
Mine are unlucky, in that my X has not been good and has refused consistent, predictable contact either by phone or visit (it has been 5 weeks now can you fathom
), and he has not been answering their questions honestly and kindly about why he is not here anymore. But he has big ishoos. And it is out of my control.
But they are thriving, their home is calmer and happier, they have boundaries and structure, they see their extended family more and we are moving closer to my family in a few weeks. They are excited about changing schools and moving, but it has been gradual and they have had many months to adjust to the idea. My family are planning on rallying around and being stable, consistent other adults in their lives, which is a relief as the children need that desperately.
I was advised to say, mummy and daddy can't live together any more, but MUMMY LOVES YOU AND DADDY LOVES YOU VERY MUCH. And to be honest without too much complicated detail.
You also need to think about yourself. You do not need to spend a weekend with your x, or have him around in the evenings etc. Make sure you are happy with arrangements, as if you get stressed this will impact on the kids. It might be better to send dad out with kids for a few hours and not go along?