Hey, howdy, hey, Susanne and welcome to the Disney Parks Moms Panel. I am so glad you asked this question so we can clear up some of the stroller confusion.
Yes, Disney released new
park guidelines for stroller size and many Guests are "confoosel" like
Heffalumps and Woozels. The policy is, "As of May 1, 2019, strollers may not be larger than 31” (79cm) wide and 52” (132cm) long and stroller wagons will no longer be permitted." It is great to know that you were previously allowed inside the theme parks with your smarTrike but, with the new restrictions, your model may not qualify. The smarTrike is a brilliantly adaptable tricycle and from my research online and speaking with smarTrike, the standard length for their smarTfold series is just over 38" and all their widths are within the guidelines. I used the smartFold 300,600, and 700 as my references and the measurements were around 38.7" x 17.1" x 39.6". If this is the case with your model then you should be able to glide in like Aladdin on Magic Carpet.
Convenient for all Guests on the ground near the parking structures and security points, are some temporary rectangular stroller guides to give you a visual. Just roll your smarTrike into the outline and if it fits inside, you should be good to go. That being said if security deems that the smarTrike is outside of the guidelines, they have the right to turn it away.
Of course, you may leave your stroller at home and rent one.
Stroller Rentals are just outside
Disneyland Park and may be used at both Disneyland Park and
Disney California Adventure Park.
Disney Dad Tip: Balloons and ribbons are some of the items we attached to our strollers so they did not get lost in the sea of infant and child transportation. I love the glasshouse balloons the best. These are the ones with a clear outside balloon with an inflated Mickey-shaped balloon inside. They are a Disneyland Park classic.
Susanne, enjoy making many Magical Memories.
~Jason