Now Prime Minister Pedro Sánchez aims to relax the rule on 27 April so they can "get some fresh air".
Barcelona Mayor Ada Colau, who has young children herself, this week pleaded with the government to allow children outside.
Spain has seen more than 20,000 deaths since the start of the pandemic and almost 200,000 reported cases.
In a televised briefing on Saturday evening, Mr Sánchez said Spain had left behind "the most extreme moments and contained the brutal onslaught of the pandemic".
But he said he would ask parliament to extend Spain's state of alarm to 9 May as the achievements made were "still insufficient and above all fragile" and could not be jeopardised by "hasty decisions".
Another 565 deaths were reported on Saturday, well down from the peak of the pandemic, and the government allowed some non-essential workers to resume construction and manufacturing last Monday.