First of all, you are not a bad mommy!
Second, you spend as much time with them as they allow and you can handle. There is no way you can be with them all day long. On the other hand, they may be content to play by themselves 99% of the day. My son is very independent and does not really care to play with me much. I try to constantly talk to him (since he is not talking yet). I try to get down on the ground and play with him for 5-10 minutes for every hour. This is the minimum, some days it is a lot more and some days it is actually less. I also try to do some things with him consistently each day. Before bed we read our books. While in the tub we work on numbers, letters, and colors (because he has those foam numbers and letters). I try and get him out of the house at least 2-3 times a week. Sometimes we will just go to the mall and walk around. Other times it is slightly more educational and we will go to the zoo or to story time. I also try to get him out and socializing at least 1-2 times a week through the mall play area, church, etc.
I hope that helps.
Kimberly