People go to yard sales looking for a great deal, and in my experience (as an occasional, recreational yard saler) you aren't likely to get the prices that you want for your items, even if they are in great condition. Some yard salers are normal or even above-average income but very frugal (like myself), and some are literally "shopping" in their price range because they cannot afford retail. Either way, they are looking for bargains.
I've read in magazines before that to figure out how to price your items, go to yardsales in your area and see what the "going rates" are that people are asking (and see if their stuff is actually selling). In the same article, it said that typical stuff would go for about 10% of the retail price - probably not what you want to hear, though I'm sure for exceptional stuff you could get somewhat more (maybe 25%?).
For myself, I was yard saling a lot when I was pregnant with my second child (and we had a 6-figure income at the time - but we were/are frugal). People would get all excited when they saw me coming and try to force all their preg/baby stuff on me. I found nice maternity dresses, skirts, baby clothes (some name brand) for like $1 a piece (without haggling - I'm not much of a haggler; if the price is too high, I'm not interested). So for me personally, I don't have any desire to spend 50% of retail or whatever, when I really can find bargains like that. I obviously do buy retail often times, but I am just as frugal there, and would only buy at 50% off or whatever, so I wouldn't go to a yard sale and pay what I could in a store. I paid $10 for a high chair (that we still have) at a yard sale, which was the asking price.
Also, I didn't necessarily need a breast pump at that time, but would inquire when people had them for sale. They generally wanted about $150 for their nice Medela pumps. I just wasn't interested in paying that much, especially since I didn't really need one (had an old one that still did the job, but was dying, but I didn't need it much so it did the job). Then one day there was one, and the lady said she had used it less than 10x, and she was only asking $20, for the $350+ model. I certainly bought it.
So, I don't know that a yard sale is the right venue for you. I think you would hate it. The non-english speakers would be offering you like $5 for the high chair, and a quarter a piece for the clothes, and you would be insulted (which is ok).
I'm not sure where you are located, but we are stationed at Camp Lejeune, and there's a huge amount of business done on lejeuneyardsales.com. You can (for a fee) post pictures of your items. Also, there's craigslist.com, which is free, and you can post pictures there as well. There's the newspaper, but that can cost quite a bit. There's also ebay, but I'm sure it's a lot of trouble.
Anyway, I'm trying to say that people who are in the market to buy things second hand are often doing so to get a really good price. But, to some, half off retail might be a good deal, especially if they are looking for that very model or whatever. So, however you do it, I would recommend that you advertise how swanky your stuff is, to hopefully attract people who are looking for higher-end or name brand things, i.e. "top of the line *brand name* high chair in like-new condidtion", and "designer clothes" and be sure to list the sizes... Good luck!