Gave notice one week ago at my babysitting job. They are having a problem finding someone. I said I'd give them to the end of April.?

Two weeks notice is standard. After that it's not your concern so either you can be a super nice person - nothing wrong with that or go about your life, again nothing wrong with that.

If you still have the time and they are still paying you, then giving them more time would seem to work for everyone. One week notice is very close to no notice at all so it's logical they'd ask for longer notice. If you've another job you've accepted that starts before the end of the month.. you'll have to put your foot down.

Giving a months notice is the norm

so its not "overly nice and accommodating"

I would however clarify that your last day will be the xxth of April as they may not try as hard as they might to find someone else if they think you will just remain