Cross-Eyed?

Mabeline

My son is 4 months and loves to look at his hands, but while he stares at it, his eyes cross. It's been maybe 2 weeks he's done this and I never really worried until my MIL mentioned that she's worried he's gonna be cross eyed. She just told me that his eye becomes lazy, as it drifts but I've never seen it happen. Anyone else experience this? I'm calling his pediatrician tomorrow. He has his 4 month shot appointment DEC 16th.