Save money? Since she not only has to pay for the child, but they need an adult to accompany them, she'll be paying $60 or $70 to go to this class. No, saving money would be to say "sorry dear, you're too young and can't join your siblings/friends, let's go ride on Nemo instead". LOL
But to each his own...I prefer that my children do activities that are something they'll enjoy and/or get something out of regardless of whether they're 9 and it's an 8 year old class or they're 15 and it's meant for college students. We let our children have interests regardless of what someone else says their age should be (or their gender for that matter...we never did do much with dolls, but we did a lot of "boy" interests when they were younger, trucks, army men, sports, etc...and now as teens they are about as girly-girl as I can stand, lol).
My children are teenagers now taking college courses (dual enrollment) so I guess they shouldn't have gone to the college and asked for permission either since technically some of the courses they're taking weren't intended for the dual enrollment program, but since they could show that they could handle the load, an "exception" was made. And I stayed completely out of it, telling them if they wanted it, they had to convince the college. My girls are in classes where 19 & 20 year olds are coming to OUR house for study time. And no, they're NOT brainiacs, just studious and ambitious and most of all hard working for what they want.
So I, guess we'll just have to agree to disagree. Because you'll never convince me that age matters enough to keep a 4.10 year old out of a class for 5.00 and above. Age simply isn't good enough of a determining factor for anything we do...and not just as kids, but as adults. I know a 67yo who could run rings about my teens for her energy, and she refuses to retire because she's loving working, but mainstream says she should have 2 years ago or more and every year she complains that her friends are putting pressure on her to retire but she won't! I'll bet she was a 4 year old capable of being with 5 year olds, lol. And my 15 year olds can hold their own and then some with kids several years older then they are without batting an eye. BUT...that's only in the classroom...they're simply not interested (thank you Lord) in the social scene of those college age kids.
AND last point and then I'm done...if Disney really cared that deeply about being sure that no one was 2 months short of the listed age range, then they'd have asked for birthdates or at least ages on the application. Then...well, then it would be lying to put other than the child's true age and then the 4.10yo should not apply, IMO. They ask the child's age when you book a room for heavens sake....of course that's partly to know whether to charge them kids or adults price on the dining plan.....but ya know they also have that so when a child turns 18 and is suddenly the 3rd adult in a room, and pay an extra fee. That's important to Disney. And if that 4 year old enrolls then Disney gets that $70....why would they turn that away. So if Disney cared, they'd ask....they don't ask, and I don't personally feel it necessary to tell them more than they asked.