Running a 12VDC lead from the TH to the toys will keep the toy batteries up. Banana plugs on the wall to cables terminated with alligator clips or quick disconnect 2-wire plugs to the toys will keep things neat. However, it does sound like you have parasitic draws on the batteries or the batteries are old and self-discharging.
To prevent the TH batteries from being pulled down, solar charging will cover up the parasitic draw. I suggest spending money on a good charger connected to your solar that will keep the batteries maintained yet not boil them out due to overcharging.
