Get lots of video's, like for toddlers and very young children that are learning their ABC's, in English. The words No and Yes (Si) are easy. Share your head when you say it or nod and they will get it fast. Porfavor is please and No, Gracias is no thank you. There are many MANY bilingual books in the library and things like Sesame Street even if they are oldwer is also good. There should be ESL classes in the school system or some transion class for them. Aqui no, means 'not here' and you can get a basic language dictionary for next to nothing at a second hand book store. Just keep it simple. It's more important for them to learn English than for you to learn Spanish so let them watch lots of appropriate tv (this is the only time I advocate this) and make a big old deal when they practice their English with you. There are shows that are bilingual like Maya and Miguel (
http://pbskids.org/mayaandmiguel/flash.html).
Get them in an age appropriate playgroup asap since interacting with other kids will be what will motivate them the most.
"En-sayn-ah-may" mans "show me" so when they ask for something and you cannot figure it out say "ensen~ame" then, when you know what it is say it in English so they have a chance to learn it. Keep doing that and always smile. Nonverbals are a LOT more important when there is a language barrier so keep conscious of your facial expressions.
Don't bend over backwards to understand every wish. Assist them to communicate their needs to you but not getting their wishes understood will encourage language aquisition and retention.
Ask if you have any more questions. Hasta luego (see you later)