This was our first experience with international travel with an infant in arms. I wasn't sure what to expect from the procedural side and had read enough blogs to know it was going to be a mess.
When we checked in for our flight in Denver we had to pay taxes for our little one for each country we were traveling to. I was unable to do this before hand, so it had to be done at check in. This took no less than 45 min for the Delta agent to call the mysterious office of children or whatever and figure out what we owed. (It ends up being about 10%of your ticket cost.) We were issued paper tickets for little H, which they need for accountability.
If you decide to check the car seat and/or stroller you can ask that they wrap them in plastic. We have travel bags for both but asked that the stroller be wrapped. On the way to the UK we checked the car seat and we checked both car seat and stroller on the way home (who wants to carry that stuff around the airport!?!)
Security in the US is as expected, see my post on traveling. Wear the baby through the metal detector, pack baby food in a bag, etc.
Once we arrived at Heathrow and collected our gate checked stroller, we were skipped to the head of the line to get through immigration. (I'm assuming due to the fact that H is so cute...and was getting cranky!) We had our passports ready and the guy had a good chuckle about the passport photo taken at 3 months old.
Just like in the US the Car Seat and Stroller came up on the oversized item carrousel, so don't wait around the other one.
Luggage trolleys are free at LHR, so grab one and use it if you need it. Plus then you can pretend you are in Love Actually.
On our way home we had the documents stating we had paid the taxes, but the check in process still took 30 min. Again, the mysterious child office had to be called. I think in this case it had to do with us being on several skyteam partner airlines. Regardless, arrive early.
Getting through security in the UK was actually really quick. I was allowed to wear H in the ergo carrier and walk through the metal detector. There was no hand scan required.
The sealed baby food posed a bit more of an issue. I've been told a number of different things in the US. Depending on the size of the pouch, sometimes it is done, sometimes I have to open it for the magic strip to be held above it. At Heathrow I was required to open 50% of the pouches and taste them - yep, put them in my mouth and eat them. Haha.
Meanwhile the rest of security was very strait forward. It is mostly automated. You scan your tickets barcode to get into the security area, which is immeasurably faster than having someone else do it and sign their name on if and stamp it....you get the picture. Shoes stay on. All electronics (including iPads and kindles) are unpacked. The conveyer belt is also automated so if your item is flagged it gets pushed into another lane for an in depth search - which keeps you out of the way of travelers not needing a more in depth search. Everyone was very peasant and we moved through very quickly.
It is certainly exhausting, but so worth it to travel with your little one!