There are some simple ways to make these without having to spend much money. Boats can be made out of milk cartons or plastic bottles. Cut the bottle or carton in half and sand down the edges so they are not sharp. Form the discarded half into a sail and attach it to a large straw. Using wax from a candle you can make this sail stand up in your boat.
Children can have boat races in the bathtub or swimming pool.
Cars can be made from the same article or from boxes. To make the wheels you can either use a long screw or dowel and poke it through the body of the car. Affix plastic lids for the wheels. These lids can come from the tubs butter comes in or other such tubs. All of these are just some ideas you can use to make toys for your children.