Need help with the kids, but not up to hiring a full-time sitter? Try a "mother's helper". A mother's helper is usually an older child who lives in your neighborhood. She may not be quite old enough to babysit alone, yet, but could use the practice and experience and doesn't cost as much as a regular babysitter (mainly because you are always around). A mother's helper can take the kids out in the backyard or down to the playroom and keep the kids occupied while you work. She can also help with small household tasks such as setting the table and getting snacks.
Need some work space where little hands can't reach? Try putting a baby-gate between your office and the rest of the house. You can still see and be seen, and "leap to the rescue" if necessary.