Likely you have a municipal agency (start with City Hall) or Extension Service office where informed persons can tell you the local practices for managing lead in soil. For one thing, growing veggies in raised beds with imported clean soil -- or soilless planting mix -- avoids removing soil and disposing of it as hazardous waste.

To locate your county's Extension Service office, use this interactive map:
http://npic.orst.edu/pest/countyext.htm

City or County Health Department.

As an env. specialist working in this exact field, I can recommend a couple things. First you will get a lot more bang for your buck TESTING your soil - both out in the yard and right near the house - than spending time and $$ tweaking your soil trying to suck up lead that may or may not be present into sunflowers and disposing of them. I mean it's a cool idea but....read on.

The soil near the house will likely be much higher than out in the yard. It doesn't migrate far from where it falls. So find out from the health dept how to get soil tested and collect composite samples in both areas. It should not cost much and may actually be free.

Finally if you want to prevent exposure to your kids, once you know what is there, covering the soil works just as well as remediating it. If it's hot near the house, consider mulch, pavers, etc. Or just remove soil in that area. Even with gardening, most of the exposure is from particles of soil stuck to vegetables (root crops, lettuce etc. are the worst) rather than actual uptake into the plant. Minimize exposure to affected soil: playing on it, digging in it. Make sure hands are washed. Simple things like that cost very little and make a big difference.

Information for the state of Massachusetts:

http://www.mass.gov/eea/agencies/massdep/recycle/reduce/lead-contamination-in-your-yard.html

theparsley makes a very good point. You really don't have time to wait. The biggest effect of Pb on the nervous system occurs before age 6. Adults are much less susceptible. There can also be fetal exposure. Get some tests done first and go from there.

I would also recommend getting the soil tested before you freak out.

Then pave over or remove dirt from the "hot spots" and have your kids wash their hands after playing in the dirt. Use raised beds for vegetables.

The REALLY bad lead poisoning comes from children with "pica", eating chips of lead paint off the woodwork in their crumbling slum. Because of the pica, they tend to eat a LOT of paint for its faintly sweet taste, much more than a kid playhing in the dirt would ever consume.

Lead dust in older houses is also a problem. Old paint gives off dust particles as it degrades, which collect in window wells and sills, and in carpets and cracks in wood floors. Not to freak you out but there are other sources besides soil and kids can have high blood lead levels without actually eating paint chips. If you have an old house with lead paint inside - even if it's covered with new paint - you might consider a wipe test of the floors and window wells. Pretty cheap to do I think.