Currently it's a random town jump, I just started and my heir prospects are a toddler and a baby at the moment. Quite excited to see how they look when they get older, and progress with the generations.
I also currently have a 100 baby challenge on hold, and a random legacy challenge. I like to have a lot of things going because I switch families quite a lot. I have a couple of other saves that aren't challenges too, so I play them every now and again. I'm also just playing the challenges for fun, not really for any sort of points, just to spice up my gameplay.
Edit: My random town jump family now have three kids, and that's enough for me! I'm loving playing them so far, and they make some cute kids! They have Willard who's a child, and Daniel and Martha who are toddlers. Daniel will be a child soon, and Willard a teen a day after that. I have no idea who will be heir at this point, but I'm leaning towards Martha right now. I'm going to post pictures of them as teens in the 'children born to original townies' thread since their parents are townies.