An article at the Wall Street Journal offers a variety of tips and advice:
Parents are complaining of airline seating policies that create "baby ghettos" in the back of planes. Even worse, families are increasingly split up, leaving small children in middle seats in the company of strangers unless passengers arrange seat swaps on board...Over 400 comments at the link, many by experienced, savvy travelers.
Several factors are at play. First, many seats on flights are reserved for elite-level frequent fliers or full-fare business travelers. Routinely full flights have less seat-assignment flexibility. Also, airlines are increasingly selling choice seat assignments for extra fees, an expensive option for families. And bulkhead rows at the front of coach cabins that used to be ideal for traveling with infants, offering more privacy for diaper changes and more space for restless toddlers, now have to be reserved for passengers with disabilities. As a result, families often end up separated or at the back of the plane...
The plane's configuration can also affect placement. On smaller regional jets, for example, some rows don't have an extra oxygen mask to be used on an infant traveling on an adult's lap. That means someone who reserved a seat and has a lap child must be relocated, splitting up a family... [it seems to me that any adult with common sense could "buddy-breathe" with a child in an emergency, but of course rules are rules]
Ms. Hoobing thinks the hardest part of travel with kids is boarding. Airlines typically no longer let families with small children board first on flights. Instead, they often come after first class and top-tier frequent fliers. Kids and parents—lugging car seats, diaper bags, videogames and toys—clog the aisles and delay general boarding. Though airlines provide leniency, such as exempting diaper bags for carry-on bag limits and waiving checked-baggage fees for car seats and strollers, they have tightened restrictions.
On June 1, for example, American stopped letting parents check jogging strollers, non-collapsible strollers or strollers heavier than 20 pounds at the gate. United already bans gate-checking strollers that don't collapse.