Baby monitor

So my husband is leaving for a month for business and we have baby monitors but I normally run in the neighborhood from 5:30-6:30am while they (6 mo old and 2 year old) are still sleeping and I want to continue doing that. Anyone have long range monitor suggestions that I could see/hear both of them? The farthest I would run is 1/4 mile because our neighborhood is circular. The only other idea I had was to call an old phone and have that near the monitors that we already have. Suggestions?