EF Core vs Aggregate Root - Is there a way to prevent persisting changes to child entities?

I'll use the common example of an Order aggregate root which has a collection of LineItems.

Because all changes need to go through the aggregate root, I add a IReadOnlyList<LineItem> LineItems navigation property to the Order, backed by a private readonly List<LineItem> lineItems field. So now we can't just do order.LineItems.Add(), but instead we have to use an appropriate AddLineItem method on the aggregate root to add the line item.

But, in order to be able to use the AddLineItem on an Order entity fetched from the database using EF Core, I need to use Include(o => o.LineItems) in my query, otherwise LineItems would be null, and I'd get an exception when trying to add to it. So what's stopping me from getting a LineItem from the read-only list and doing changes on it, and then persisting them using DbContext.SaveChanges()?

Is there a way to prevent this?

You should make your setters internal on LineItem. Then the only entities that can change them are those in the same assembly, e.g. the Order.

All requests to change properties of the LineItem should be routed through the Order, which can then enforce invariants and use internal setters to update the LineItem (or even use internal methods on the LineItem, which takes care of updating properties with private setters).