public class UserControl1 : UserControl
        {
            private bool _isMouseEntered;

            public UserControl1()
            {
                InitializeComponent();

                MouseEnter += UserControl1_MouseEnter;
                MouseLeave += (sender, e) =>
                                  {
                                      _isMouseEntered = false;
                                      SomeLeaveAction();
                                  };
            }

            private void UserControl1_Load(object sender, EventArgs e)
            {
                InitEvents(Controls);
            }

            private void InitEvents(ControlCollection controls)
            {
                List<Control> controlList = controls.Cast<Control>().ToList();

                controlList.ForEach(control =>
                                 {
                                     control.MouseEnter += UserControl1_MouseEnter;
                                     InitEvents(control.Controls);
                                 }
                    );
            }

            private void UserControl1_MouseEnter(object sender, EventArgs e)
            {
                if (!_isMouseEntered)
                {
                    _isMouseEntered = true;
                    SomeEnterAction();
                }
            }

            private void SomeEnterAction()
            {
            }

            private void SomeLeaveAction()
            {
            }
        }