The reason you are working from home is so you can spend more time with your family, right? So don’t feel guilty about scaling back your work commitments whilst the kids are off school. If they are old enough, ask your kids to help you to honour your commitments to your clients so you can give them time too. You might even find that they are willing to help you with your work if it means that you’ll be able to concentrate on doing fun stuff with them. An example might be that they will give you quiet time in the morning (or even deliver brochures) if you’ll take them to the pool in the afternoon.
Make sure you’re really present when you’re spending time with your kids. You can’t be constantly interrupting your time with them to answer your phone or check e-mail. They’ll recognise that you are only half there and resent it. Unplug and really give them your attention when you’re spending time with them.