Select children based on parents which are selected by another expression

I have heavy query written in another function as expression, by which I can select parent, but how to use this function to select children based on results?

public class Parent
{
    public int Id { get; set; }
    public string Name { get; set; }
    public DateTime Prop1 { get; set; }
    public virtual ICollection<Child> Childs { get; set; }
}

public class Child
{
    public int Id { get; set; }
    public int ParentId { get; set; }
    public string Name { get; set; }
    public virtual Parent Parent { get; set; }
}

I have function to select parents:

private Expression<Func<Parent, bool>> SelectParents(
    DateTime start,
    DateTime end,
    List<string> names = null
    )
{

    if (names == null) names = new();

    return x => x.Prop1 > start
        && x.Prop1 < end
        && (names.Count > 0 ? names.Contains(x.Name) : true);
}

When I use it to select parents – it works just fine, but how to select children based on this expression?

var parentCount = await _dbContext.Parents.where(SelectParents(.....)).CountAsync();

>Solution :

await _dbContext.Parents.Where(SelectParents(.....)).SelectMany(parent => parent.Childs).ToListAsync()