Dealing with direct play

Hi all, We've just moved to 11v11 and up into a higher league with some physically large and strong sides. Our oppo at the weekend played to their strengths which is height and strength. Their keeper kicked from his hands 100%. His kicks cleared the half way line comfortably. All free kicks from 10 yds short of the halfway line saw their big centre backs coming up into our box for the high delivery. Their centre backs were very comfortable heading away our clearances ( only a few but enough to show up the discrepancy in ability to handle the high ball). My son is one who would head long high balls up the middle but even he stopped after 5 or 6! He was centre back and at a conservative estimate he would have had 10 to 15 more he shied away from. It's obvious that they carried on because it worked. My question is, short of waiting a few years for my team to catch up, how can I prepare them for this approach given I've been reliably informed this is not uncommon in the strongest teams in this league? Especially given relatively recent heading guidelines. All help gratefully accepted