Reported to Police

Hello.

Please I need your help. I just feel totally lost at the moment.
Last Friday Ive got an sms from my Ex to say that my Son has said I have hit him and there is now a Polisanmälan against me.
Of course I haven't hit the boy and would never harm my kids.
I love them and care for them very much.

We have 50/50 Custody of the kids ,and on Friday she would not give me my son or my daughter and just told me they are afraid of you.
I know thats not true.

My daughter has tried to make contact with me the weekend but her Mother has told me to stop trying to make contact with her.
Its a terrible sad situation.
Im getting no answers and can't see my children.

Can she keep the kids like this even though we have 50% custody each?
Can she keep my daughter from me even though she isn't involved in this?

How long will this situation take before I can see my kids again?
I just feel so sad and so does my Wife.

Please help me .

Thank you/