It's hard. Unless you've got really close family or friends to help out, it's really difficult unless you work in a field where flexible working/working from home is realistic and you have an understanding boss.
I work full time. I don't have any family so I use a professional CM to do after school/holiday care. Before my DC started school I used a mix of the CM and a nursery. Both forms of childcare were wonderful. I chose them carefully and never regretted my choice. However, there are quite strict rules surrounding illness and if you only have professional childcare to rely on you will end up taking some time off for illness. That's where you really need a good boss and friends/family who can step into the breach at short notice. I am under no illusions that if I hadn't had the boss I had, I would have joined the ranks of single mothers on benefits.
Only 1 in 5 working mothers rely on professional childcare. I suspect that tells its own story.
I don't mean to alarm you - after all I've managed it so it must be doable - but definitely do your homework. Plan on who you're going to use, have a backup, think about what you'll do in emergencies, find other parents who can help you out in a fix, and find out company policy on time off for sick DC etc (legally they have to allow you to have it, but if you have more than they deem normal they can let you go as a result and many will insist on you taking unpaid leave, while others may be more generous).
Try not to think of it as working for nothing over the holidays. For a start, your DC are 50% your DH's, so he should be paying half, but also keep in mind that work is about more than just money, it's about independence and challenge and can have significant effects on your self-respect, fulfilment and long-term earning potential, especially when your DC get older and childcare doesn't cost as much.
Good luck. 