I agree with the others in that the seating issue isn't what really caused the "lost" property ... And I think we all know that.
Here's my actionable suggestion for you - and yes, it takes some leg work on your part (and I might offer as a suggestion that if age appropriate you involve your child as a learning process/experience)
Physicaly go to the United counter at your home airport and speak with a Supervisor there..
Explain the situation to him/her.. And then ask *nicely* for the physcial station phone numbers of either EWR, MUC or both - BLQ is a non-UA served city, so their "presence" there will be a partner presence, therefore your options limited..
Each airline also has internal departmental codes that they use to better define departments and to facilitate the sending of intra-company email, parcels and even intra-carrier messges.. In many cases, a carrier lists their internal phone directory not by "plain language" text, but by this two-letter departmental code.
These codes can vary based on the carrier.. What Thai Airways here in Bangkok uses is different than what United uses or what Singapore uses..
What you want is their local phone numbers for the station operations office or customer service; and for UA, those codes would be EWROZ or EWROO and in the case of MUC, it would be MUCOZ as that's a smaller station.
United, like most carries does not want or encourage the public to phone local stations.. They're just not set up to handle incoming phone calls as most of the airport people are operational; they spend most of their time out of the physical office and in "the field" be that at the gates, on the ramp, etc.. So don't be surprised if your request is denied..
When, and IF you can and do get into contact with EWR or MUC, ask to speak to a Customer Service supervisor or equivalent.. These folks are the ones who will be in the best position to know what they actually have locally on-hand, and put you into contact with their local L&F clerks (who commonly are a part of baggage service)
EWR is a huge hub for UA, so you might have to try several times.. MUC is much smaller.
Again, this process isn't easy and requires some leg work on your part, but largely its the best way to speak to someone locally whose is actually there to see what is or is not on hand.
Do remember that carriers aren't liable for passengers' left on board items, and rightly or wrongly, they don't expend large amounts of labor or resources to this reunification effort, so bear that in mind when and if you choose to go down this road.
Edited: 7:55 pm, April 07, 2013