I Have 3 children, oldest is 6 yrs old, there father walked out on them just over 3 yrs ago.
They use to have contact every second weekend at first, then I noticed the behaviour pattern would change for atleast 3 days after, so I put a stop to contact until my children are old enough to cope with the situation.
To be honest it has done them the world of good, But they don't actually ask about there real dad.