Swallowed - not. My 1st did put anything into his mouth. Second - the was putting everything since the dawn of ages. To the point that I was always holding her hand in all those playgroups. And all the stuff was lit "Oh, you overprotecting her! Oh, you don't let her investigate, it will show up on her development!". No way, better safe then sorry!. Anyway, by the age of 3 (when free nursery was starting) I was more or less ok with her being in the nursery and not putting something wrong into her mouth.
As for A&E, been there a lot of times, some of them were false alarm. Feeling guilty? Yes, some of the accidents could be prevented. But it's life. Nothing seriose has happend - fantastic, take it as a losson so next time you won't get into situation like that.