When is too early to make your kid walk your dogs?

Lincoln has always expressed interest in the dogs leashes and trys to walk the dogs at home. While we were at the cabin this past weekend, we let Lincoln attempt to walk the dogs. Yes, he did get pulled down a few times but our son is resiliant and wanted to keep doing it.  Since he will at some point weigh more than the dogs, maybe we can let that be his job. Could be years before he out weighs Baxter!