I have 5 children, 3 girls 25, 21 and nearly 18, and 2 boys 23 and 12. I don't know if there is an 'easy' age to tell you the truth. It seems that just as you take that deep sigh and kick back a bit, something rears its head and you find yourself saying "oh I wish they were XX again, it was so much easier'.
As newborns, while they do sleep a lot, they don't seem to sleep when 'normal' people do and you find yourself exhausted wishing for the age when they slept through the night.
Then that age arrives, followed closely behind by teething and grabbing for everything and you wish they were newborns again, just lying there and smelling so sweetly.
Then they start to walk and you're finding yourself constantly chasing after them, they don't want you to carry them anywhere, which can be a hassle at times and you wish they were back just sitting in the middle of the room playing contentedly.
Then they start school and you think ok THIS is the best age ever, but then they come home telling you about the bully in their class that you'd like to take that bully behind the wood shed and have a discussion with them, their friends are being mean to them today when yesterday they were best buds. They want to wear the latest fashion, come home saying words you never say in your home, has a boyfriend one day & then he's stupid the next day. And you feel that some of their innocence is slipping away and you wish they were back as a toddler just running and playing.
Then they hit PUBERTY and you wonder if your child has been replaced by pod people!! At about age 13-15 they are going through changes faster than Elizabeth Taylor goes through husbands. Suddenly you as the parent 'don't understand them' and they don't hang on your every word like they use to. They want to be independent but still they still need you and that bugs them. Their bodies are changing and they go through this awkward stage and the boys voices are cracking & changing, the girls are starting their cycles (if they haven't already), they're both growing hair in strange places and all the while trying to 'keep up with the Brittney's/Justn's' of this world. They cry more easily, get angry quicker and need you more even if they don't ask or act like it. And once again you find yourself reflecting back on the day they started school and thought you could do no wrong.
Then they get into high school and WOW, lots going on there. They are driving, planning their futures, 'finding themselves' and while the explosions of puberty are no longer there, you find you're not as close to them as you once were and you miss that. They get up, go to school, come home, homework, then out the door in the car going to friends or to the mall. They no longer want to hang out with the family as much as before, their friends are such a big part of their lives now. They start looking at boyfriend/girlfriends as possible husbands/wives so when they have break ups, its very hard on them. They are trying to find their place in this world and you are trying to keep them from losing their way. And soon they graduate and they're off on their own and you pray that what you've instilled in them values and skills to make it in this world.
Now they're on their own and you think whew---my parenting is done. Think again. You see them making choices that you don't like or understand and it makes you question your parenting, it makes you feel like you failed somehow. But you realize you didn't fail, because at some point you know that its their life, their choices and you've done well to give them the ability to make those choices. Sometimes those 20 somethings come back to the nest and you realize you can't parent them like you use to because now you have an adult on your hands. And your relationship changes and you long for those days back in high school when you could set the curfews and execute the consequences. Instead you come to an understanding and both parties work within that.
But as I now look back on my life as a parent for the past 25 years, I wouldn't change one thing. I would never wish NOT to be a parent despite all the heartache and work involved because when that 20-something writes and tells you how much they love and admire you, when that high schooler crawls up in your lap because they want your comfort, when that 12 year old brings you flowers he picked himself--you forget all that and just cherish the right now. So just cherish the right now because before long it'll become that 'oh I wish they were XX again' moment.
Hope that's not too long.