I can't speak for Ryanair but easyjet never allows young children to be say apart from their parents. This is covered in the cabin crew manual. Families do get split up if they are literally the last to board a full flight but the children aren't split from parents.
Either way allocated seating, I'm told, will be announced by months end. Anyone who works for an airline will know that whilst it will be a step forward, you can rarely satisfy everyone's seating preferences on a full flight.