Do they have a ISBN #?

Size doesn't matter... well, in this case, anyway!  They're ok to post (ISBN or not!).

N C,

This is a section from the help center on what is postable or not postable.  The question about children's books is at the bottom.

Pamphlets/Booklets/leaflets without ISBNs: NO

• These sometimes contain advertising; members also complain at having to pay a credit for these.
• Leaflets = non-children's books with less than 20 pages
• Booklets = non-children's books with less than 50 pages
• Leaflet/pamphlets/booklets with ISBNs may be posted
  • if so, the number of pages must be included in the item description.
• Children's books do not count as booklets or leaflets, even if they are short. 
  • Children's books can be expected to have short pagelengths and the booklet/leaflet designations do not apply.

One thing you could do if they are really small is offer more than one of them in a deal for only one credit.

Just a thought, but if they have an ISBN they should be postable.

the only thing that will be affected is what you pay for postage...there is a size restriction on media mail...

Christy, are you sure about that? There is a weight limit but I never heard about any other size restrictions. Besides if the books are that light, they could be mailed FC.

Media Mail doesn't have a minimum size or weight, but there is a thickness minimum for Delivery Confirmation, 3/4". The weight limit for MM is only at the top end, max 70 pounds.

There's this: Books, including books issued to supplement other books, of at least eight printed pages http://pe.usps.gov/text/dmm300/373.htm#wp1015205