If you have a Child Arrangements Order and the other parent is not adhering to the terms then they are technically in breach of the order. However; you are able to go agains the terms of a Child Arrangements Order if there is a reasonable excuse. A common reasonable excuse is if there is a safeguarding concern (harm could come to the child).
The Coronavirus is a fairly unprecedented occurrence and the courts have had to grapple with a fairly novel situation. The President of the Family Division issued some guidance on this situation and you can read this for yourself here: https://www.judiciary.uk/announcements/coronavirus-crisis-guidance-on-compliance-with-family-court-child-arrangement-orders/.
As you can see from the guidance, parents are being given a lot of discretion. Whilst it is hoped that parents will use their best judgment and only make decisions in the interests of the child; there will inevitably be parents using the situation to their advantage.
In principle, if a parent is stopping contact due to a genuine COVID-19 safeguarding concern then the court is likely to "excuse" this breach. The court is going to be slow to punish a parent who is doing their best for their child.
If you have reason to believe that she is taking advantage of the situation and you think you can persuade the court that this is the case then you could apply to enforce the order.
You use a solicitor to apply for you and you can find a family solicitor here: https://solicitors.lawsociety.org.uk.
If you want to apply yourself then you can find the form here: https://www.gov.uk/government/publications/form-c79-application-related-to-enforcement-of-a-child-arrangement-order.
Try to engage in some dialogue with the other parent if you can first. If they have genuine concerns then try to "think outside the box". Can contact take place via video calls etc instead? Could you go out with the child to the park etc rather than take them home. Court orders are made without the foresight of these types of events so sometimes you have to agree between you different arrangements. So long as you both agree variations that is fine.
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