Commuting through an area with heavy drug use, seen a couple syringes on the floor. does drug residue get tracked into my car/yard via the bottom of my shoes. if so, can that endanger my toddler when he is playing and drops toys to bottom of car?

I consider the risk in the situation cited to approach zero. Of course you should avoid areas of such use when you can, but you have more risk from the drug users than their residue.

For peace of mind, wear boots over shoes, and take them off and leave in your car before entering house. Store boots in a separate container and clean them off weekly. No transfer of residue will occur since you are being careful, but look out for possible needles and remove them with pliers, don't touch them and dispose them in a solid container.