Hi R.
My babies are 18 months apart (now 2 years and 6 months old) and we got the Phil & Teds E3 stroller with the add-on seat when my youngest was born. GREAT STROLLER! What is so neat about it is that you can use it in multiple variations for whatever combination of children's ages you have. When my youngest was a newborn, we had it so she would lie flat underneath the add-on seat which easily attached to the front. and when she was old enough to sit up at about 4 months, we switched the add-on seat to the back and sat up the main seat where my son (2)sits in the front and she sits in the back.
the neatest thing about this stroller is how small it fold. It is really well made and has a decent sized basket. the handle is really nice and ergonomically correct as well as adjustable (we are a tall couple and this was a plus for us). it is super thin in width also, which is the opposite of the side-by-side strollers that are available. this makes it so much easier to go shopping, to museums, travel...
This stroller is super well-made! The material is really durable and easily cleans up. It is the easiest stroller that i have ever used. easy to steer, easy to fold, light enough to pick up and throw into your trunk without a struggle. and it fits in the trunk too!
There are some draw-backs. My biggest complaint is that you must be sure to have the heavier child in the front seat when you have it in the add-on-seat in the back configuration. if you have a child in the back seat without someone in the front, it will tip over backwards which is dangerous. I have figured out that you can always counterweight by placing a bag or purse or whatever you bring along with you, in the front seat. My other complaint is about the sun-protection. there is a small canopy-cover that is basically one-directional that only covers the front seat partially. if you are walking towards the sun, your child will be in the sun. and the back seat doesn't have any cover. sun from the front or back is not a problem here, but from the sides, it is full-on. I have learned to bring two lightweight blankets to strategically wrap around different parts of the stroller to create more sun-coverage. it works for us. Lastly, this stroller is also expensive!!! Oh, make sure you get the new one with the wheel guards.
after all that i have said, I would still recommend this stroller. I love it and don't plan on needing another stroller.
good luck shopping,
C.