Don't be afraid to keep working. Being with children full-time would drive you nuts; you need time interacting only with adults, for your own sanity.
I recommend that you hire a foreign-born nanny.
Require the new nanny to always speak her native language to the children, even when your daughter/son insists on replying using English. You could go further and ask her to refuse to respond when the children fail to use her language.
This might seem like it would confuse your kids, but young children are well known to learn new languages much more readily than older kids or adults. Like music, languages are things that young children learn much better than older kids or adults. Start your kids now!
Hopefully the nanny also can use children's books to teach your children to read that language.
You can ask your nanny to repeat her statements to you in English when it is important for you to understand what she just said to your kids.
This guarantees that your kid will be bilingual. This has many benefits (see website links below).
After you look at the website link, and hire that nanny, hopefully you will feel really good about the many benefits you are giving your kids by doing this while continuing to work. You'll be glad your children are spending time with the new nanny!
If I were you, I would seek a nanny speaking a language that's very widely spoken worldwide, but is seldom taught in your country. That way, the language skill will be rarer and more valuable. Arabic? Mandarin Chinese? If you have trouble finding such a nanny, hopefully you can at least hire a Spanish or French speaking one; I assume they're more plentiful.
If you cannot get a good referral from somebody you trust, then search using Google for "au pair" or "nanny". You should see several websites devoted to connecting nannies looking for work with parents. And putting an ad in craigslist.org or monster.com could work well also.
Of course you would want to spend the first day with the nanny while she takes care of your children. And you should install a hidden camera in your home (if the nanny will remain there); every once in a while, you can fast forward through a day's worth of recording to look for misbehavior.
A related recommendation: It's valuable to find a daycare/preschool that offers foreign language immersion, if any of them offer that in your area.
Also, some areas have schools that immerse the students in a foreign language, starting in kindergarten or the first grade. Check the website of your local district, or call them, and see what language immersion schools they offer. Although you would not be enrolling your children for several years, you can plan ahead to do that.
Play dates with other children could really help. Ideally, the new nanny could help you find children who speak her language, and set up play dates with them. That gives your child extra reason to try to learn the language.
After a while, your children would easily speak the school's language, the nanny's language, your language (if you choose to speak a foreign language to the children), and the language of the geographic region where your kids grow up.