You can always keep putting air into the tires, replace the valve stems, replace the tires, or use something to goo around the stem as a temporary fix till a later time.
Got a slow leak in your tire and can't figure out where? It is likely a worn core in your tire's valve stem. Replacing it is easy, fast and best of all, CHEAP! The local garage will likely hit you for their hourly shop charge if they do it. about 3 minutes and $1. 49!