Honesty is the best policy.
You can be honest about it, but be prepared of the repercussion effects in terms of the impact on your career progression. Given the constraints on your job flexibility, it's not going to do good to your job stability in a difficult market environment as well. That said, I'll pick my family over my career anytime.
Assuming that your boss is understanding and pro family, have a discussion on the possibility of changing your job profile such that it's likes time sensitive and allows you to plan ahead.