Hi, 

We don't think that this is anything too concerning. It could be either a little leaf anthracnose which is very common on many shade trees (sycamore, maple, oaks) or it could just be a little sun scorch on the new young growth as it is leafing out. 

You can pluck off those browned leaves in the mean time. Anthracnose is and fungal disease that can happen especially in wet weather like we had this spring. Removing the leaves will help keep the spore from overwintering for next year. Typically if this occurs in large trees (where you can't easily reach the leaves) the tree will shed those damaged leaves and re-leaf around mid summer and be fine. If the tree is otherwise healthy and not stressed it isn't a detrimental disease to the trees. If this occurs when the tree is larger you can rake up any fallen leaves and send to any county compost system as the hotter temperature will kill off any pathogens or spores. Home composting isn't typically hot enough to do so. 

We can also notice some further health adjustments that you could take to help your young tree grow. You can untie and remove the staking for the trunk. It is better to let trees develop a strong root and trunk system by allowing them to sway in the wind. Staking a tree can also lead to a girdled or choked trunk if the ropes/string/wire material gets too tight and starts to cut into the bark. This can kill a tree or embed the material in the trunk and cut off the flow of nutrients. If you feel like the tree bends over with the weight of large leaves, you can try some webbing rope which is flat and loosely wrap it around the trunk to stake. The link will show you in the photo how to properly use the staking ties. Make sure it is still able to move and sway. 

The link provided for staking also has directly on planting. See if you can pull some of the mulch away at the base and reveal the root flare at the bottom where it connects to the soil. It can be a little difficult to see on young trees but the trunk should come straight down then flare out at the bottom where it meets the soil, like a stem of a wine glass. Trees that are  planted too deeply can developing roots along the base of the trunk that can eventually starting wrapping around the tree as they search for oxygen and girdle the trunk. This could cause a weak point in the tree that could break in a storm or develop infection of disease or an insect problem. Also try to taper the mulch into the trunk but not have it touching the trunk to cause it to be too wet against the bark. 

If you have further concerns please reach out. 

Emily