First dream - Looks like you're concerned about where you're going in life. The dead children may symbolize past regrets (or regrets of things you haven't done)...or they could be parts of yourself that never got to come to life before they had to be repressed. The car having flipped over I think is circumstantial,. The point is that only you can get you to where you need to go, hence you having to walk.

Second dream could be your anxiety issues affecting your dream.

The third dream seems to be twofold. First is the acquiring of a subconscious desire - that your dog was still around. The second part is the acknowledgement of your need for connection (a connection your dog probably filled). But this need has to be kept secret, hence you had to put the dog in the basement. Something about it seems unclean....wrong...to you, or you fear that that is how others will see it. So you want to purify it and make it right (like with the bleach).