This exactly. If my parents or inlaws wanted to set aside money for my LOs on a regular basis, to accumulate to a lump sum, I would want them to get full credit for their generosity!My grandparents opened accounts for each of their four grand kids when they were born. On our 21st birthdays we were all given access to them. They each had a set sum of money in them. I'm not exactly sure how they managed saving in them, but I am pretty certain they put maybe £10 per month in each of the four accounts - it was more a gesture of getting a lump sum on our 21st birthdays. My eldest cousin bought driving lessons and insured his car, the next cousin bought a car as he could already drive, I bought a nice piece of jewellery and then lived off it durin my final semester at Uni so I could quit work and focus on my career.
We also had individual savings accounts which my parents opened for us, but that was a more short-term saving account which we used for things like spending money on holiday, my sister an I even chipped in and bought a computer from that account when we were young - that is where any birthday, Christmas money etc went which was completely different from the trust account my grandparents gave us.
I can't understand the issue personally,
If it's a matter of perceived competition, ie one set of grandparents being a lot wealthier than the other (as in my own case) then that's something that will have to be managed/explained throughout your children's lives, and they should understand the situation clearly by the time they're old enough for access to a trust account.