Take a look at taxcalc.eu - this should help you to get an idea on your income.
The 50K gross of your husband (taking into account kids and your tax credits) will result in a take home pay of just under 40K a year (or 3300 a month)
If you add the 30K gross, the net pay increases to 60K a year (or just over 5000 a month), therefore a difference of 1700.
Taking into account the childcare costs of 1200, you have 500 euro more in the pocket. Maybe that is just a "few euro" for a 40 hour week - but you will also have PRSI contributions.
Also, I would also try to recommend working for a variety of reason apart from money.
Giving your tax credits to your husbands makes only 150 net difference per month, as he is not paying much tax anyway (not much being relative of course)