I have 2 who went off to uni and built their futures within their respective uni towns. They come home to visit 3 or 4 times a year. I love to see them but after a few days of long legs, big feet, and their shoes, clothes, bags and other bits cluttering up the place I also love to see them go again.
Number 3 is 16. It may be harder to see the baby fly the nest but I'm sure I'll get over it quickly.
With mobiles and social networking sites it's easy to keep tabs on them and keep updated with what they are doing.
After years of ferrying around teenagers at all hours of the day or night plus going through their teenage angst with them there comes a time when parents need peace, solitude, and a clean, tidy home without the never ending bickering and competing.
I can't wait for the day when I can book a holiday for 2 and do exactly what we want to do during the day and evening without waiting up, worrying what the teens are getting up to or what time they'll be in.
Or even arriving home from work to a quiet, clean house, making food for 2, getting into pj's and just chilling. It will feel strange but oh so welcome 
