The existing childcare vouchers scheme is closing to new entrants. The replacement scheme will be less beneficial for some people. If you want in to the old one, you need to act now, because your employer needs to process it in time for April.
This is particularly relevant to new parents. I'm on mat leave at the moment, but my employer is letting me 'buy in' to the old scheme with a nominal sum, just so I can get in under the wire.
This explainer from Money Saving Expert is very helpful in deciding which is the best scheme for you.
www.moneysavingexpert.com/news/family/2018/02/want-childcare-vouchers-apply-now-to-make-sure-you-beat-the-april-deadline