Generic With method builder

GenericBuilder.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;
using Xunit;

namespace Tjoelala
{
    public class Person
    {
        public string Name { get; private set; }
        public string FirstName { get; set; }
        public string FullName => $"{FirstName} {Name}";
        public int Age { get; set; }
        public List<Person> Kids { get; private set; } = new List<Person>();

        private Person() { }
        public Person(string name)
        {
            Name = name;
        }

    }

    public class PersonBuilder : ObjectBuilder<Person, PersonBuilder>
    {
        public PersonBuilder()
        {
            With(x => x.Name, "Bos")
            .With(x => x.FirstName, "Jos")
            .With(x => x.Age, 44);
        }

        public PersonBuilder WithKids(int nbOfKids)
        {
            var kids = Enumerable.Range(0, nbOfKids)
                .Select(i => new PersonBuilder()
                    .With(t => t.FirstName, $"kid{i}")
                    .With(t => t.Age, 14)
                    .Build())
                .ToList();
            return With(t => t.Kids, kids);
        }
    }

    public class UnitTest1
    {
        [Fact]
        public void Test1()
        {
            var person = new PersonBuilder()
                .With(t => t.FirstName, "Albert")
                .With(t => t.Name, "Bosje")
                .WithKids(3)
                .Build();

            Assert.Equal("Albert Bosje", person.FullName);
            Assert.Equal(3, person.Kids.Count);
        }
    }


    #region Object builder stuff

    public abstract class ObjectBuilder<TObject, TBuilder> where TBuilder : ObjectBuilder<TObject, TBuilder> where TObject : class
    {
        private readonly Dictionary<PropertyInfo, object> _values = new Dictionary<PropertyInfo, object>();

        public virtual TObject Build()
        {
            var obj = Activator.CreateInstance(typeof(TObject), true) as TObject;
            foreach (var kvp in _values)
            {
                var pi = kvp.Key;
                var value = kvp.Value;

                pi.SetValue(obj, value);
            }
            return obj;
        }

        public TBuilder With<TProp>(Expression<Func<TObject, TProp>> expr, TProp value)
        {
            var body = expr.Body as MemberExpression;
            var property = body.Member as PropertyInfo;
            _values[property] = value;
            return this as TBuilder;
        }

    }

    #endregion
}