Absolutely! It only takes some discipline and planning. If your household has both Spanish and English speaking members you should try to have one parent speak one language while the other speaks the other. For households with English speaking only parents you can use tools such as videos and CDs to expose your child to Spanish. Do your best to have them spend some time every day listening to Spanish.
If you can find other families in your area that speak Spanish organize play dates and encourage the children to speak only Spanish. If the kids are uncomfortable doing that (mine are not comfortable speaking Spanish in front of other people) have them watch movies, videos (Featured Products) or listen to music in Spanish. Also, just being around a group of adults speaking Spanish can be beneficial.
I was frustrated for many years that my children were not speaking Spanish back to me even though they understood most everything I said. However, I noticed that as my oldest got to be a teenager she started using it more. I feel as if the Spanish was always in there waiting to come out at some point. All those years trying so hard to expose the children to Spanish was worth the effort.